I use a Epson 1640SU Photo (which means it's got the Transparancy Adapator lid) which is a generation or 2 before the above mentioned 2450. It's a 1600dpi scanner. It does up to 4x5 film scans, and does a good enough job with 35mm for previewing and web use. This could be a $30 ebay candidate (remember to factor in shipping as they are relatively large). It also does good quality and quick flatbed scans.

Some examples :

35mm
http://unite.com.au/~u3819a/gallery/images/candid03.jpg
http://unite.com.au/~u3819a/gallery/...ndscapes04.jpg
http://www.nlandgl.com/usefilmdayout (all)

MF (645)
http://unite.com.au/~u3819a/gallery/...bstracts04.jpg
http://unite.com.au/~u3819a/gallery/...uildings04.jpg
http://unite.com.au/~u3819a/gallery/images/nature01.jpg
http://www.photocritique.net/g/s?zzahAc-p22165230