I paid (including financing) $14k 17 months ago to a Mitsu dealership with a warranty for my '01 Eclipse Spyder GS. Now I believe the KBB value is around $8k-$9k (I shoulda bought an '00 for the right spot on the price curve, but that's another story). you should be looking at less than that if you're buying it from a private seller, especially if it needs obvious work.

Brake conversions: (I'm in the middle of this myself, got rear discs in my garage waiting to go on).

It depends on how far you want to take it
Rear discs you can find parts in 2 places:
Club3g.com Automotive For Sale threads
M&S Recycling is is where I bought my backing plate w/parking brake (~$80) after getting calipers from a club3g member (~$100)
I also strongly recommend Road Race Engineering for Stainless Steel braided brake lines (~$80)

Any 00-05 will work for Rear discs, also 2G non-AWD DSMs have the same backing plate and calipers. Read up more on the swap on club3g

Front GT Dual-piston Caliper Discs
The catch here is that there are 2 different calipers for the '00 and the '01-'05. The later calipers are smaller and cheaper, everyone strongly advises the '00. The real nastiness is that rotors for 1 do not fit rotors for the other, so know which ones you get. Again, you can try to find somebody selling front calipers on club3g, but people really pounce on those (especially '00 calipers) and alot of the time, people ask way too much money for them, might be easier to buy new (I don't suggest trying junkyards, GTs are rare finds, and finding a '00 is about a 1 in 6 shot).

Rotors and pads are available either from any source as normal, if you want slotted rotors and performance pads, I recommend this group buy by Performance Parts Store these people do lots of good stuff to bring aftermarket to a car that doesnt get much aftermarket at good prices.
'00 Powerslot Rotors and Hawk pads $375 shipped front and back.

Other common upgrades for the 3g:
Polyurethane bushings available at Road Race Engineering
Performance struts and Lowering/Performance springs available through a PPS group buy
Suspension Techniques Rear Sway Bar
Strut tower braces for coupes

I drive the sport shift as well, it's quite nice, if you do decide to go FI, you will need to have an Import Performance Transmissions rebuild kit installed to tighten tolerances. The kit, local store installing the kit, modifying my Torque converter, then sending the valve body to IPT for modification ran me about $3200. It was an unexpected expense of FI to me, so I pass on the information to you.

Any questions, anything else I can answer or explain (to the best of my ability) just PM or post. I'm no expert, but I've been working on this thing for a while and am happy to share my experiences with it.