Money isn't really an issue, I've been using GameSauce's business strategy that effectively allows me to generate money continuously, in fact in preparation for this I earned about 5 mill to buy upgrades, because CaliMeatWagon's spreadsheed said that 4.5 should be enough. Surly not worth all that money since you will use it once and forget that it even exists. You just match 4 pictures to copy a finger print or you get a mini game where you have to remember a pattern of dots. If you played the first heist (fleeca) you already know how the drilling works.

Still, if you have only enough of money for two of those I would advise to keep that money for something that's actually useful, like a new vehicle or anything else you want to buy.

Its not like a vault door could disappear after every heist, that makes no sense.

I haven't finished the heist yet but I'm almost 100% the things you buy stay there.