I've looked into every single company offering this service and each one makes it sound cheaper than the last but add charges somewhere else to get there money back.
rental charge
set up fee
pci fee
Minimum monthly charge fee
phone call charges
transaction fee's
insurance fee
commercial cards have a higher charge rate
some other card types are higher i.e. american express etc...
i even had one guy swearing that that was it, he's told me every charge there is and thats what i'll pay, i then mentioned pci to him, and he said "oh yes but that doesn't go to us, thats a seperate matter"
also be carefull that your length of contract with them is not different from the length of contract with the equipment, some companies get you to rent the card reader from a different company without telling you. and they then say that your only tied in with them for a year, but forget to tell you that the equipment is rented for 5 years.
its a minefield out there i tell ya, so do your homework, read the small print and get everything in writing from the rep.