There are a few 3.8 6G75 motors on eBay - a FWD application might need some parts scrounging and a little extra effort to make it work, but would be way more budget friendly than a 4.0, and the extra 300cc should give a noticeable power increase.

http://www.ebay.com/itm/ENGINE-2004-2008...0db&vxp=mtr

http://www.ebay.com/itm/2004-2008-Mitsub...80f&vxp=mtr

http://www.ebay.com/itm/06-07-MITSUBISHI...907&vxp=mtr

http://www.ebay.com/itm/ENGINE-06-07-MIT...12c&vxp=mtr

I'll be doing something like this if my motor ever dies.