Gentlemen, if I may offer some advice as a non-trad who worked in a coat-and-tie office for a couple years after college, I know that buying dress clothes can be pricey, especially for the college student/recent college grad of limited means. If you're looking for shirts and ties, I'd suggest eBay. As far as shirts, if you know your size (15.5 and 34, in my case), you can go to the Dress Shirts section, plug in your measurements, and see what comes up. Generally, you can get some great deals, especially if you don't mind wearing a used shirt (as long as it's in great condition, of course). As far as ties go, just type in a particular company (I'd try Brooks Brothers, as mentioned above, or Ralph Lauren - both are pretty conservative but classy) and see what's available. I've picked up a few ties from there, from the companies I mentioned above, and they were all less than $20, including shipping.
If you need a suit and can't quite afford one from a store in your area, I'd suggest hitting up used/vintage clothing stores. Look for a suit that fits your shoulders and is in your size (for me, 40R or 40S). If you find one that fits your shoulders and has pants that fit your waist, get it. You can take it to a tailor and pay them $50 or whatever, and they'll cut it up so it fits your sleeve and pant lengths. I also did this, back in my coat-and-tie days, and got a couple suits for $20 each at a Goodwill, then just had them tailored - all in all, it cost me about $70 a suit. This generally will only work for people in a decent-sized city, though, with a good handful of vintage/used stores to peruse. You can also find some suits on eBay too, but just be sure that the sellers have a "Return" option, so if it doesn't fit, you're not out $300 or whatever. And actually, eBay does have some nice Brooks Brothers suits for a fraction of the cost.
That's my advice. Obviously, if you can afford the new $500 suits or your parents are willing to help out, go that route. But just wanted to throw out my experiences to give some of you others some guidance.