Depending on your inseam, height, riding style, etc. a 26'er may be more appropriate so a 29er is not the only option. Under 30 lbs. is relatively common for FS 29er's.

3K will get you a lot. I've purchased two used 29er's (roughly 1 year old) off eBay (one hard tail and one full suspension), both combined for less than 3K total. My full suspension bike is an '09 Turner Sultan which new in the configuration I got would cost 5-6K. The best time to shop for a bike (new or used) is late fall or winter when the demand is significantly lower and your chances of finding a bargain are greatest.