S4 will cost you $$$$ to get into the low 13's - modding Audi's is not cheap
The Legacy GT (turbo) is nice, I'd consider that or the WRX.
The GTO will SUCK in the winter - just as bad as a Mustang.
With your limitations I think you only have two cars to choose from, unless you want to cram your ass into an SRT-4, or perhaps look at a 1.8T GTI
