Hey Joe, welcome to the site.
Glad to see that you are going to update the classic and get it on the road again.
There's just soo much to cover that I can't do it all at one sitting so I'll start with what I know best - the LSx stuff.
There is a new issue of Chevy High Performance on the market, see if you can pick it up. It breaks down ALL the LSx motors and their derivitives nicely. I think it's also at the main page of their website http://www.chevyhighperformance.com
For learning purposes, I wanted to make sure you are familiar with these sites too:
(serious LS motor stuff there...and a small forum for transplants),... www.pro-touring.com
(my home away from home).
For parts - there's a ton of stuff at S&P Performance, they cater to the LS transplants. www.hotrodlane.cc
The good news is that A) You can't go wrong with any of the LS-based motors and B) no matter which motor you pick, you still need pretty much the exact supporting parts. eg. motor mounts, ECU, radiator, tranny's and hydraulic clutch setup's for the 6 speed, LS headers, etc.
Like Dave mentioned above,.....there three main sticking points to consider in making the motor fit under the hood.
1. Oil pan. Most people buy an aftermarket pan, some modify (cut/re-weld) a stock pan, and I think I've heard of a person or two using the F-body oil pan. (not sure what car they had, perhaps a camaro)
2. Accessories. Truck accessories sit high,...too high. those brackets are no good. F-body brackets work for most people. Corvette brackets might work, but may interfere with the sub-frame cross-member depending on the car.
If you will have A/C,...some folks use a special bracket that allows you to mount the A/C high on the passenger side. Iinstead of low...where it may hit the frame)
Also, some folks just notch the frame and are done with it. That's ok too.
3. Intake manifold. Truck motor intakes are tall and ugly. If you find a standard car intake for your motor you'll be fine.
So, you're right, the prices in your area are WAY out of control. You can pick up a used LS2 or L92 motor, complete for around 3500-5000. LS3's maybe a little more.
New motors with no accessories or ECU/wiring harness go for 4000-6000.
T56 transmissions can be had for around 2000. $3000 new.