Great suit (wish it were my size)! An excellent example of Pre-Prada Helmut Lang. As such, the quality is considerably better than more recent suits. Good luck selling it!
Although, just from my experience, I think that $275 might be a great buy-it-now price, but might be a little high for an opening bid. After all, Prada bought Lang in 1999, so the suit looks to be at least 7 years old. Please don't read that as an admonishment, because honestly $275 is still a pretty fair deal for the suit. But, I've found from experience that Lang suits can be a difficult sell, since Lang's biggest buyers are generally young and buy many more tshirts, jeans, sneakers, and hoodies than suits.
As such, if you had an opening bid of around $125-150, you would probably receive bids up to $225-$250 or so. Of course, it is always impossible to tell and as such you might get bids up to $500... but if it doesn't sell the first time around, this would be my recommendation (having sold a number of Lang items over the past couple of years, the suits of which always sold for less than the tshirts, oddly enough).