I am interested in this as well. Authorize.net is just too expensive compared to going through a merchant account provider like Card Service Internation that uses the linkpoint gateway.
If your looking for a cheap merchant account check these guys out.
http://www.cardservice.com/
$10.00 a month, no gateway fee, 3.49 %, .35 per transaction.
I think this is probably the best deal out there as of right now.
Doug