First of all, use Craigslist. It's your friend. Here's a rundown of things I've gotten:
I got all of the following from a Gold's Gym via Craigslist -- they had done some remodeling and had stuff to get rid of:
Precor club quality treadmill
Rubber floor matting: ~300 sf 1/2" thick
Dumbbell pairs, from 15-60LB
2x 9' long dumbbell racks
The rest got from various sources:
375LB rubber-coated free weights (barely used): $75 (worth about $600 easy!)
Home-made pullup bar from 2"x6" / plumbing pipe: >$50
Home made 'slam ball': >$20
Crossfit bar: $145 (only thing I bought 'new')
Squat Rack/Weight tree: $25
About 500+SF of Swain Gold premium wrestling mats (for martial arts/bjj): $1100
125LB 6' Heavy Bag: I think $100
Still to go: Concept 2 rower, bumper plates, and I'm making a sandbag out of a duffle bag/sand.
I got most of this stuff as an absolute STEAL from Craigslist... just be diligent and patient.