Are we talking suits only, or the more commonly required "business formal"?
I get coupons from Jos. A. Bank and Men's Wearhouse (which are now the same place) via mail and email - they are among the best stores to get ties, because they have an enormous clearance section of very high-quality new ties for $20 (which is about the cap I'm willing to pay for a tie). Accessories there are a bad idea. The pants quality is fine, shirt quality is fine, but both are very expensive unless you get 3 or so at a time when they're on sale with your coupon etc etc.
If you go to one of those places, though, you'll get your sizing covered and can buy the bulk of your stuff online, or as Zamboni suggested, a Goodwill in a ritzy town. I can't remember the name a colleague of mine uses, but places like
http://www.thesuitdepot.com/mens-suits.htmldo full suits for not-completely-bonkers prices. You'll have to look around though - the trick is to find an online retailer that does your size properly, if you go that route. Be prepared to be disappointed with how long they last - folds will fray between 1-2 years on any dress shirts I've ever had. I probably spend 400-450/year on everything (shoes, watches, tie clips, shirts, pants, dress socks, shoes, ties, rare dry-cleaning favorite ties that got messed up). Don't freak out about ironing - pull your clothes from the dryer as soon as it stops and hang them up and you won't really need to get an iron.
Do not buy wool pants. Or anything. They're too expensive to care for.
(I'll post the site my colleague actually vouches for when I can get an answer from him tomorrow)