First off, here's the link to the save files:

https://drive.google.com/file/d/1csSufruTLgV-r__6Gc8-Sqis-J5HCTm6/view?usp=sharing

To install them, you'll first need to disable Steam cloud saves.

Then, you need to go to your steam install directory, not the game's install directory, but steam's own directory. You then need to head to Poly Bridge's save folder in userdata. Here's the usual location: C:\Program Files (x86)\Steam\userdata\your steam id\367450\remote

Unzip your pants the save files you downloaded and paste them into the folder.
⚠Warning⚠, this may replace your current saves unless you choose to merge the folders.

Now, just load the "Under Budget, Under Stress" save.

If you instead want the save of a specific level, go into the game and make a save within that level. Then, close the game and sort the savefiles folder by "date modified" to see what that level's folder is called.

P.S. this doesn't contain the Area 52 levels in it for my own sanity, but those levels also aren't required for the achievements.

If you've loaded a save that doesn't work, there's a good chance it will after a few reloads. The physics are wildly inconsistent to the point where you might see at least 4 completely different results. If the save doesn't work after like 10 reloads, it's possible that the game is throwing a tantrum and refuses to take the solution, so turn on stress visibility (T by default) to see what's breaking and adjust it slightly with the grid off (G by default).

Also, this is for version 1.1.0 of the game, the most recent version. I doubt that this game will ever get updated again, but if it does, most of the bridges probably won't work. Also, if you somehow have an older version, the bridges probably won't work with that either.

If you are having trouble with my save games appearing, you may need to create a save in the level beforehand, then copy my save to overwrite your prior one. Thanks to Darker The ashes for bringing this to my attention. Also thanks to Askalon08 for confirming this fix.

Around a quarter of the bridges are my designs, but then my brain gave up and I resorted to walkthroughs. I used a few videos, though I don't remember which ones, and this guide was a huge help:
https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=1238663408
If you have any questions about anything, feel free to ask.