First off, let's go over things that DON'T count for level completion:
Any stealing won't count, you need to smash things. That's the whole point of the level.
Also, no lamps count for whatever reason, this includes the big chandeliers and the small lamps on the walls.
Using grenades to clear rooms will not always give you the full amount you would get for smashing things individually. Specifically the pear store has a limit of 5 headphones at a time, and the wine store has a limit of 10 bottles at a time.

Buying the gas can asset and burning a store gives $5600, regardless of which store. The fire doesn't actually destroy any items in the store, but all the stores you can burn are ones with only a cash register in them anyway.

Everything here is worth $500. Every piece of glass, regardless of size, the two signs (circled in yellow), and the big shield. It only counts if you break the uppermost part of the shield though (circled in red).

Inside, contrary to the outside, there's practically nothing to destroy. We have another one of those signs, as well as a wall-mounted version (circled in yellow again) which shows up on walls all over the mall, and two glass doors, everything still being worth $500. That's it. Note that the upper windows (circled in green) and all lamps are worth no money at all for some reason. Not even the cash register here is worth anything.

The signs (circled in yellow above) appear throughout the mall, are worth $500 each, and have an interesting bug. They don't have a trigger to stop them from being destroyed multiple times, and because of that they can actually be worth as much as $1500. They award $500 when shot, $500 when smashed with a melee attack, and $500 again when blown up with explosives. They give off sparks each time they are "destroyed".
This isn't very useful since it's not that much money anyway, and it's not really practical to destroy things several times, but it's an interesting bug and if you have the chance to both smash and shoot one: go for it!

Store front windows are where most of your progress is going to come from. The big windows are worth $800 each, the glass in the doors $500 each, and the small upper windows $250 each.

Another good source of repair costs is the glass ceiling. Every "piece" destroyed gives $800. Also, these high windows (circled in red) give $250 each, unlike the similar ones at the entrance. The chandeliers, as I said earlier, give nothing.

In the shoe store the stacks of shoeboxes (circled in yellow) give $250 for the small ones and $500 for the big ones. The whole stack counts as one and it doesn't matter where you hit it. The shoe displays (circled in red) work similarly, with the three shoes counting as one and giving $250 if you hit any of them. Also, the cash register gives $500, like most cash registers. Single shoes in the window displays only give $40 and really shouldn't be bothered with.
Total: $5480

In this store EVERY SINGLE ITEM counts as one, and hitting any one of them gives $500 after which destroying any more does not add anything. The cash register is worth $500 as usual.
Side note: Because of a bug the window above the door is worthless.
Total: $1000

Nothing but the cash register in here.

Nothing worth bothering with in here except the cash register. The products come in groups of 3 or 5, with the group being worth either $40 or nothing at all. The glass in the displays is also worth $40 a piece.
Total: $1900

This counts just like a store front, with the upper windows being worth $250 each and the lower $800, even though they're so narrow.

First of all, the glass railings are only worth $80 a piece and shouldn't be bothered with. Apparently they're not even needed for the achievement!

Not a lot to smash in here, with the glass in the displays being worth just $80. The cash register is still $500 though, and there's quite a lot of loot to be had. Because of a bug the glass in the wall of this store facing the center path is not worth anything.
Total: $1700

Now this is more like it! Every single bottle, EXCEPT for the ones circled in green, is worth $250, and the cash register is $500 as usual. All in all it's a whopping $25250!
Side note: An interesting bug is that the big window on the same side as the worthless bottles is only worth $250 instead of $800.
Total: $25250. Note that if you grenade this room, you will only get $3000!

Another two stores with nothing but a cash register.

$250 for each bag hit in here as well as $500 for the register as usual.
Total: $6500

Nothing breakable in the gym except for the cash register. Not even that big nonreflective mirror.

This wall (between the gym and the pear store) is interesting. The high windows are worthless, but the the upper windows on the wall are worth $800, just like the lower ones. And the glass in the doors is indestructible.

Another gold mine! Every pair of headphones, both on the wall and on the table, are worth $250. The laptops work in a very strange way: the "computer part" is worth $250 ONLY if you shoot it before the screen (the screen goes black when the computer is destroyed), while the screen is worth $330. And on top of that there are two cash registers.
Total $20320. Note that if you grenade this room, you will only get $4570!

The car is the main attraction here. The huge window is unfortunately still only worth $800. The car itself is worth $6000, but takes quite a lot of damage to destroy. Just shoot the car anywhere but the windows, and look out for a big puff of smoke coming from the car which signals it's been destroyed. The rear view mirrors are worth $1300 a piece. The car windows are very strange, with the front window being worth $1300, the rear window being worth $800 and taking a lot more damage than any other window, the right window being worth $500 and the left $1300. The side windows can also be destroyed twice (if there's broken glass left in them just smash it again), boosting their worth to $1000 and $2600 respectively. This makes the maximum you can get out of the car $14300 if you destroy it completely. And of course there's our old friend the cash register.
Total: $14800. Grenading gives you the full amount!

The short version is to focus on smashing store front windows and the glass ceiling. Grenading the car gives you a lot of money quickly, and the best shops to focus on are the wine shop and the pear store. Secondary choices would be the shoe shop and the bag shop.

If you think I missed anything or have anything to add let me know. And have fun smashing stuff!