If your guy wants a challange then but a level ten stage 2 or 3 rebuild kit in. It uses your exsiting tranny but with all new parts.
Here is the link.
http://www.levelten.com/store/import...rts_subaru.htm
I did a 4.11 impreza tranny swap and it cost about 1100.
As far as a mt5, small cars has a complete kit.
http://www.smallcar.com/svx/5spdkit.htm
It is all up to what you want.
good luck
Steve