My rct experience was similar to geos one. I had a root canal and a permanent filling on a molar (no crown discussed at that point, but this may be due to different standards in dentistry in my country back then). I even chew normally on that side and the whole thing was working for 6 years till a piece of it broke off and a crown was suggested. Even the broken tooth managed to hold for several months till I had the money for a crown.
This is an extreme case, I had a lot of luck and deffinitely wouldn't recommend you to wait that long, but the point is that if you need a bit of extra time to get your crowns, it doesn't necessarily mean that you will lose the teeth.
Not chewing on that side and trying to get the crowns as soon as possible would be the right way to go.
It might be a good idea to ask your dentist about how to make the teeth as resistant as possible for you to have enough time to save for the crowns. He/she might also tell you how much time you have. Your dentist must be familiar with this problem, it's not unusual not to be able to pay for a treatment immediately.
