Very sad and very pathetic when you consider what the hourly rate of the pilot you are checking/training will be getting when flying the line; even an F/O will be on more than that. A full session is, unreality, 6.30-7.00hrs, plus preparation time and travel time. In fact, if flying in/out it could cost you 2 unpaid days; and let's not forget the overtime night/weekend element that is also unpaid.
However, if Boeing and other ATO's around the world are paying €500- U$650 per session there is not much the freelancer can do to negotiate. The important element is expenses and travel. I had a request for services from one agency, but all travel & accommodation was own cost. If you are flying in/out that deal is a non-starter. You'll be losing money.
On another thread, JetBlast, there was a discussion about solicitors fees where the cartel philosophy demands £250-450/hr, even for a junior. Makes you wonder. The difference is the solicitor tells you, the customer, what the cost will be. For a TRE the ATO customer tells you the TRE service provider what the remuneration will be. If you ask what you think you are worth they will seek someone else. Sadly there seems to be no alternative to take it or leave it.