Many ISP's include a fax2email service in their 'value-added' services. The only proviso is you use it at least once in 3 or 6 months (varies between suppliers). They get their fees from your fax no being a national rate number, it costs you nothing.
All the others lke eFax and YacFax and the like use geographical STD's, impose no limits but they are subscription based services, i.e. you pay.