Picture posting is enabled for all :)
The plot is worth what people are willing to pay. If 90% of plot holders pay what they are asking you may find they do not renew your contract next year - and offer it to somebody on the waiting list who is willing to pay the new fees. Have you checked neighbouring sites to see what amenities they get compared to you, and at what price?
Surely to use market forces to price allotments out of some people's reach is the antithesis of what allotments are meant for?