I might be wrong, but it sounds like you took your car to Autobarn, which is a parts store. They came out and looked at it, and offered to sell you some parts. Perhaps they exaggerated the costs because they want to err on the safe side. Either way, you need to see a mechanic. If the guy offering to fix your car doesn't have oily hands from working on cars, you need to find help elsewhere.
I agree, the costs estimated are far too high. Castor rod bushes - $100, Steering boots - $40. You could probably get a decent set of second hand rear coilovers for $300 as well, which are best to source from a jap parts wrecker as if they're leaking/blown you can agree exchange (try to make this arrangement prior to purchase).
As for the leaks, just put some cardboard on the floor where you park, monitor the oil and other leaks, and track down their location yourself if wanting to save cash.
Also, do as much research as possible. READ A LOT of technical articles and learn about your car, or you will either:
a) be ripped off by unscrupulous people in the trade who get a sense of how little you know; or
b) have to be spoonfed all the information you need while lacking true peace of mind of how things are running so you could enjoy your driving with safety and confidence.