They have a vendor on ebay that has a quality current controlled Beck zapper for 1/2 what Sota sells theirs for. Beck said the zapper parts cost the price of a pack of chewing gum. I got a couple from SilverSmoke research for $75 and $80 (no one bid). Original improved Beck design. Plus I use 9.6 volt paintball rechargeable batteries, so the unit puts out very good output.
The site you linked has very good prices on a Sota unit but the order link does not work.