I'll throw in my .02 as well.
Brakes:
I use Muskegon for brake systems when needed. One thing you should know is just about all the vendors use Lone Star calipers, that are rebuilt GM's with SS sleeves. Go to Muskegons site and you'll find the current price on a complete kit- should be about $400. If the rotors are missing the rivets then someone was in there so you have to mic them up. range is 1.215-1.250" I toss them at 1.220 min. Next you have to find out how they are going to install things? are they going to dial in the rotor runout to under .005"( I set my under .003") Are they going to replace the hoses? What about the PB setup?
Rear Bearings-
Rebuilding cost depends on who does them and how they do them. The ones I build runs about $375 each but that doesn't include new arms,rotors, or spindles if needed. The bearings are set to .002 +/- .0005" USA Timken bearings are used. BTW, this is not a solicitation for work I'm just informing you so you can ask questions to your guy.
Differential
These can be rebuilt several ways, from the very common and lowest cost( $500-$600) to custom blueprinted better then any stock unit (up to $2k) or even drag race 12 bolt setups (3k-5K)
Front suspension and steering
Again, what is done and how it's done. Rebuilding the suspension with the common kits( chinese parts) is cheap but then so are the parts. Lower ball joints failing under 10k miles is a good example. Using MOOG brand parts 3x the price. I just bought MOOG ball joints and idler arm~ $205 compared to $165-180 for the full chinese kit. MOOG parts are no comparision to the imports. Steering boxes,you can find them all day long on ebay and vendors. Based on what I've seen, read, and was sent to correct I wouldn't use any on a wagon let alone a vette. A custom box with new gears is in the $500 range alone, add a rag and you're over $600.
Exhaust, Frame prep and paint( no welding?), suspension bushings in the strut rods, shocks, and misc parts - $700-$800 or more?
If using the best parts,custom rebuilding, and installation $7,500 may not be far off. Using the cheapest common parts, doing average rebuilds and maybe cutting some corners it could be much less in both money and quality.
I can link you to a lot of info on doing most of these jobs. Out of respect to this forum I won't list it here. If you want it,
PM me and I'll get you there.
As mentioned learn asmuch as you can on the work and how it is done and can be done before making your decision. Some guys "marry"their cars so cost is not a concern only the best jobs is, others get into a money pit they'll never get out of.
Good luck, if you want to talk it over. PM me and I'll give you my number.