I've noticed that HostCharge only charges $12 for chargebacks, or $5 if you go with the higher rate and get their chargeback insurance.

Is this unique? Are their similar 3rd-party services that charge lower or NOTHING for chargebacks?

Just for the record, HostCharge doesn't offer chargeback insurance any more. By default all clients with a good track record and a decent volume get $5 / chargeback at no extra cost :)

Regards,
Asher.