Lowest i can remember taking on a card is about the £2.00 mark, but we take payments of over £500+ on card payments quite frequently.
The more money you put through your card provider the better the deals they will give you.
Sounds like the new parented Yale with the tapered shoulder or it the lock is fitted in a security escutcheon or handles and you need to grind or file away the back shoulder.
Looking for some blanks as pictured. I have found the locks on Ebay listed below.
http://www.ebay.com/itm/BORDER-86200-Russia-High-Security-Double-Bit-Lever-Key-Door-Lock-3-Keys-/231572582830