I have just had the same letter. When we started using them back in 2002 it was a straight up front purchase of the software and you paid a nominal amount for support. It does seem an outrageous hike in what they charge and I wonder if they are pricing themselves out of the market for the smaller trader. They seem to be modelling themselves on Autotrader's business model.
I will also be looking around at the alternatives. Not impressed with them at all