Have you considered the Legacy GT wagon? I am personally looking at picking up a Legacy GT sedan right now. They have the same block and head as the STi, but is just detuned a little bit... by flashing the ECU they can easily get up over 300 hp for less than a grand. I don't know if you have done the research into tuning the Subaru's, but here is a good place to start
http://www.cobbtuning.com/main.html
Personally it is a no brainer for me to make sure the car has the 2.5L engine instead of the 2.0L engine. I like the nimbleness of the Impereza body, but that is about it... the legacy is much more comfortable and practical for every day use IMHO. Are you planning on modding this car for track/street use or just using as is? The legacy gt w/ stick is just as fast as the wrx stock, but handles a little worse due to the larger size. The weights of the wrx and legacy are surprisingly similar though... just a thought.