I would be weary of any company that doesn't outright put their TOS on their website right off the bat. There are probably hidden charges they're not stating on their website -- its usually the case.
Its better to NOT go with the cheapest... but to go for the most reliable.
Check out Humboldt Merchant Services : http://www.hbms.com/hbms/default.asp
They're the company that Charge.com uses (among Card Service International).
Except you would go right to the source, where as with Charge.. you're going to just the reseller.
They'll match any merchant's fees (for the most part), and they'll get straight to the point with you -- no run arounds.
Here's there info: