You want something out of a 1G DSM ('90-'94 Eclipse/Talon/Laser) if you are going factory Mitsubishi. A factory 14B will be around $100-$150 used for a clean used one. A small 16G is the same thing as a 14B, but uses a different, better flowing compressor wheel. Look to spend $150-$300 on a good used one. A big 16G uses a better flowing exhaust housing and exhaust wheel, usually good for around 350hp in DSM's. Its a good spooling, good topend turbo all around. Look to spend around $600 new, and about $350-$500 used.
You could also go with a TD05 or TD06-20G, but I'd only advise if you plan on building for more boost. The factory T-25 in the 2G DSM's is practically useless IMO, unless you are running some sort of SOHC-T on low boost (6-8psi). They don't really flow jack squat and poop out quick in the top end.