Bench fees: typical procedure and rates for visiting students?
If somebody is going to charge me money for a service when I'm visiting an off-campus site (or even something on-campus), I want to know about it in advance. The first thing they should have mentioned in any sort of response—or post on a website—is that it's not a free service. Without such information, people can't make an informed decision whether or not the service is worth the cost.

So I would certainly question this invoice and its fairness. (As for the cost, that also seems a bit high, but I can't really comment on a "going rate" for such a service.)