I’m not sure whether to view this as expensive or OK as I don’t really have a frame of reference re. MTB events but I’d say it’s about in the middle compared to other sports.
A typical fell race entry fee will be anywhere from free to £20 but most are in the £5 range. A road race can be anything from £10 upwards – the Great North Run costs £50 for example. Road sportives are typically in the £20 – £30 range.
Then you have the organisational setup: is it someone just doing a low key event as in most fell races, something like the Three Peaks is an exception and is the £20 example above; or is it a professional organisation: Pennine Events and Evans Cycles are behind many road sportives for example. I don’t know if Evans run their events as a promotional tool for their stores or it’s a separate financial operation that has to pay its way.
There’s quite a lot of work that goes in to organising something like this (actually a lot of work) along with hiring of all the kit like the timing chips, insurance. Each will take a nibble out of the entry fee. By the time the costs are removed and you work out the remainder any profit will probably work out at less than the minimum wage if looked at on an hourly basis.
One think I’d like to see (and this applies to all the above type of events) is a profit and loss sheet publicly available. This would let everyone decide if they are being ripped off.