The cheapest i know is True Ops - 10 %.
FBA reimbursement software is no longer allowed. I heard some sellers who used one got suspended.
Yes — there are some Amazon FBA reimbursement services and agencies out there, but finding ones that charge only about 7-8% is rare. For example, Seller Presto offers an “Amazon FBA reimbursement service” and claims to use a “low commission rate” and only charge when they recover funds. sellerpresto.com Also RefundPros does full Amazon FBA audits and recoveries (though their standard commission is more like 25%) refundpros.com, and GetIDA is one of the better known ones (though I couldn’t confirm their current rate).
I use getida, their was already 25% but now they also add min 50$ monthly if their commission less than that.