It depends on how much power you want. The carb & header are easy bolt-ons & might give you anywhere from a 5-15% power increase and for the money, that's pretty cheap power. There's not a lot more available in the way of bolt-on power other than a freer-flowing exhaust system. If you're looking for more power than that you'll be looking at some serious dollars to build a non-turbo 2.6 that would make the same power as bolting up a turbo 2.6 would. (well, not quite a bolt-in but closer than building a new motor)

I'd be willing to bet that a non-turbo 2.6 making 175 horsepower would be virtually impossible to drive on the street due to the high-rpm powerband that it would have.