I may be talking out of the wrong part of my who knows what (and I'm sure Don will correct me really really quickly if I am) but this may be an application of ETP2.
James, do you have a spec for what you need? If it's not that much beyond listings and input forms, than I imagine it can be built, or at least prototyped in ETP2 relatively quickly.
Well, that is to say, you can throw some weight into helping to build ETP2 and then you can build and prototype everything quickly. :)
talli
