A suit probably couldn't hurt. Since it's not an office job, you might just want to go with dress shirt, slacks, tie, and a sportcoat. You could even ditch the tie and still wear the sportcoat... the coat adds a lot more than the tie does, IMO.
The most important thing re: suits is to get a dress shirt with a big enough neck. A lot of suit-related discomfort comes from people wearing old dress shirts that are too tight in the neck now that they've put on a few more pounds. You can wear t-shirts for about as long as they stay in one piece. Dress shirts need to be changed along with neck size, or they will make you absolutely miserable. Get a half-size larger if you want.
Personally, I'd advise against the Stafford dress shirts. Not as comfortable as others I've tried... you can get the George branded shirts from Wal-Mart, cut out the tag in the collar (worst place to put a tag) and you'll have a very comfortable shirt for a good price. Or you can buy one from Jos A Bank. They've got good shirts and they put the tag out of the way... they also charge accordingly. They have a sale on at the moment on some of their suits, not sure what the shirts are priced at. Don't pay $100 for an off-the-rack dress shirt when you can get the Hemrajanis in Hong Kong to tailor one to your exact size for about the same price.
http://www.mytailor.com/Goodwill and the Salvation Army tend to have a decent collection of suits/sportcoats and dress shoes in excellent condition and very low prices. You'd probably be better off finding a sportcoat than a suit that fits - the previous owner might've had the same shoulder width, but a larger waist, or he might've been six inches shorter...
Very good chances of finding excellent dress shoes, unless you're an odd shoe size. Shoes are usually $10 or less... probably the best deal in the store, unless you happen upon a Ralph Lauren purple label suit for $50 or so. If you do, buy it and ebay it ASAP.
No experience with Men's Wearhouse, just Jos. A Bank. For best impression, walk in wearing a tux and a gun, looking for a bowtie to complete your ensemble.
JAB has sales all the time. Don't buy a suit from them at 'regular' prices. Wait for a 60-70% off sale and get one then. Not much more expensive than a Dillards or JC Penny suit, but they tend to be a cut above.