actually the GT-S is not going to be a rip off...or not as much as you think. Remember they are different engines, a great deal more different than you may think. The GT as you know is the economy engine which has a narrow (I believe, 33.1 degree) valve angle while the GT-S has a wider valve angle (43 degree angle; one of the main differences between the economy and sports engines)...amongst many other differences. In the long run, performance wise, the GT-S is a much better setup and a different beast altogether. The engine has more than just more horsepower, it has much more potential. So anywho...if you're wanting performance than it's the way to go hands down. If gas is the concern (and you still want the celica) then get the GT.
Here's a page with lots of good info comparing the two engine models:
http://www.everythingcelica.com/tech/_engine.html
As you can see from the above page the setup of both engines is different enough to at least consider the GT-S model celica.
Note: And if you end up getting the GT-S, you may find me at your front door pandering for a spin around the block......with me driving!
j/k! LOL