Honestly the best way I've found to get a nice suit on the cheap is to get one on eBay and then have it tailored. I used to have to wear suits for work, and being the cheap sort, this is what I did.

You can get cool vintage designer suits this way.

I would get ones roughly my size (not smaller) on eBay and take them to Hong Kong Tailors on Broad st.

I got Armani suits, Hugo Boss etc for under $100 a piece this way, including the tailoring.

A suit has to be tailored to look good anyway, so why not get 'em used?