The only flatbed machines at your price point I have sold (I really wouldn't bother with the sheet feed only units) are the HP 5510 (now discontinued) and the HP 6210 both of these have a 20 sheet ADF on the scanner. Both should be available within your budget. The only differences I can think of are that the 6210 has a better control panel and a USB Pictbridge socket.
Also be aware that some manufactures *cough* Lexmark *cough* Epson *cough* Have a habit of advertising Fax capability on their low end machines when that capability is provided by software (not on the machine)
We have sold a number of the 5510's and a few of the 6210's and had no complaints so far.
As far as I know basic printing and scanning is supported on both of these units by the HP Linux Printing Project http://hpinkjet.sourceforge.net/ this project alone, to my mind is a compelling reason to go for a HP unit (at least they are trying)
I would quote you for one but I know for a fact that Misco are underselling me on this product by a reasonable margin at the moment.