There is one - I have seen it in the shops. It's not talked about much in the forums however, as it is not worth it apparently. I'm sure the package was called Fs2004 Regionals or something like that, and it had a few a/c in it, mainly props, the 757 was the biggest.
I have asked about it in the forums of AVSIM as I would like a payware 757, and the payware companies (PSS, PMDG, Level-D) seem to take ages releasing anything (it's understandable).
Anyway, I can't remember it's name, but there is one out there and it's not very good quality. I would advise putting up with the 767 download from Level-D site - it's well worth it. If you really want a 757, POSKYs is fantastic.