Useless replies LOL
And the mustang wont give you the mpg at all
Subaru will probably blow up (the engine) because of the previous owner, not always 100% right but any wrx or sti owner will have reved the car a lot of times to 6000 rpm ++ which is not smart for the engine life time.
The audi a4 or a6 will have 200k + mileage for that price and maintenance will cost you a shit ton of cash
Toyota celica is a good choice but be wise in your choice...
In my opinion try to get a mazda 3 2.3 litre 4 cylinder 2006 - 2008. I have looked for cars in montreal and I could easily find a mazda 3 2007 ish for 13k CAD with under 60,000kms standard and in good conditions with all the gadgets (sun roof, 17" rims, spoiler, small body kit e.t.c.) You will get power, especially standard. You can also tweak the engine, (p-flow, cold air intake e.t.c) to gain a few HP here and there that wont totally wreck your engine and make your car sound beast when shifting
(Or you could look at 2002 - 2004 mazda 3 speed if you are stubborn and want 50hp more absolutely)
http://www.citymazda.com/en/usedcars/listing/index.spy?make=MazdaYou could also go for a VW Golf R32 2004 if your seriously looking into speed, but then again like I said for the previous cars most of the car owners pushed theirs to the limit, and will probably need some heavy maintenance soon after you buy it..
Another car you could go for is the Honda Civic Si, fast reliable sporty e.t.c. but it wouldn't be my personal choice...
Don't go for the above, not worth it especially the subaru, I have been smashed upon with my own "im getting a new car thread" previously and I have summed up what the others have said in my thread... (Kinda)