Yeah why does the certification process cost so much is one question I have. Would this be a conversation if the cost of the test were more reasonable?
Most likely it costs a lot because there isn't enough frequency of demand for it for more than one company to offer the service thus there is no supply. However, as it is a regulatory requirement the severity of demand when it appears is near infinite.
Having done UL certification before, this is exactly how it is.
During the process we forgot/missed that the product serial needed a single letter appended to the end to denote that it was the UL compliant version. We caught this after paying $15k for just recertification with new parts, no testing, only paperwork.
We went back to UL and told them about the mistake. They charged us $5k to open a new case just to append a "-5" to the name of the product on a handful of documents.