Ive had two Impreza's, a WRX with PPP and an STi. Enjoyed them both at the time but much prefer the Zed now, in fact its the best car ive owned.
For 1-2 years old you should be able to get a MY06, or MY05 GT4 (like mine) with the 296bhp engine. Car up to and inc 2005 (with exception of the GT4) had 280bhp, the new 2007 model has 309bhp.
Have a look on www.pistonheads.com, lots for sale on there - thats where I found mine. I wouldnt be too concerned about 1 owner personally, mine had two owners, but doesnt really make much difference on a 1 year old car still under warranty.
Personally, I would say running costs are similar to previous subaru's....