The dynomax true dual conversion pipes are $50.
You can probably get a used aftermarket catback on craigslist for around $200.
Get a stock GT catback for maybe $50 or less. Get two used aftermarket mufflers for about $40 each. The thrush mufflers he mentioned above would be a good choice as well. The exhaust shop will have no problem mating 2.5 mufflers to the stock 2.25 GT pipes, if 2.5 is what you happen to find used.
Install should be about $100.
That's what I would do. I'm a cheap bastErd junkyard/craigslist extraordinaire. I buy everything used.