Q: There's a bolt broken off the rear upper control arm the cross member

It depends. If only a bolt needs to be replaced, the price "sounds" high but even that response is speculative because there might be a lot of disassembly work to get to the bolt and then, of course the wheel alignment will have to be verified. If the control arm or other components got damaged you would need parts. The only way to determine if the price is reasonable is to get a second opinion from a certified Mechanic. If you want a second opinion, and if you go with the opinion the repair can commence right then and there, just simply request an inspection and the responding certified mechanic will get this taken care of for you. Of relevance, too, whatever the issue turns out to be, getting it repaired on a mobile basis, through YourMechanic, will almost always save you money due to the elimination of the shop overhead and other needless costs. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.