I got Mackenzie (the bear) and I did not spent money in game until latter.

I have gotten all from the events.
Played about 10 hours a day (mostly waiting in Background)
Didnt payed a Cent.
Only used the free Rubies.
Have over 1.000 left.

50 Rubies are enough to get through an Event one to two days before End.

But OK, I have the experience of the other game for these events ;)

I got both guys (Xianyun and Mac) without spending any money. I just used free diamonds that you get from the daily check in.

Depends on what you count as 'life savings'. Starting Day #1, you can get them if you spend a bit of stashed gems (what was it? like 24 or something for the modest event pack? don't remember) check in every few hours (except sleeping, obviously), & upgrade semi-efficiently (don't use event currency to buy gifts, unless it's like, the last task or 2 & you don't have time to gather enough game-money). Supposedly, you can get them completely free, 0 gems used if you follow a guide with militant precision, but I haven't tried.
Have to pay progressively more (gems and/or money) the later into the event you join.

I just barely cleared the requirements for Xianyun, & I think I got Mac a bit easier, though still using some gems (combo of experience + I think they adjusted the requirements slightly). Definitely easier if you've played the game for a while, & can stash up 50~ gems between events without having to give up on upgrading things in the main game, so if you have trouble you can try to bail yourself out. Also, there's a parallel event guide in the walkthrough section that's very helpful to skim for getting a rough idea of what to prioritize (very possibly the only way I beat the 1st event).

I never spent any actual money on either of the event boys, and I only spent diamonds on Xianyun because I started his event a day late. Spent no diamonds nor money on Mac and got him with over a day to spare. It's all about spending your time blocks effectively. When I go to sleep, I put most of my timeblocks into hobbies, then I switch them to jobs when I wake up so that the money comes in while I'm away for the day. Then, when I come back, I reassess and determine where my timeblocks need to go (I usually prioritize the hobbies and jobs that are needed to make characters level up, then hobbies that are needed at a certain level to unlock jobs and event prizes). Hope this helps for the upcoming event boy!