Seriously though, a pony club superstar that is capable of showing to a decent level, could be 5 figures.
A safe but perhaps not supermodel type IM has the right figure, a little less if there are any maintenance issues, history of lami so restrict grazing etc
I would say it all depends what you're looking for in said pony ?
A show pony first ridden type will be ££££s. A genuine, safe PC first ridden type won't be cheap either, they are a very sort after type - there seem to be far more lead rein or second ponies around and good first ridden ones are often sold by word of mouth and not advertised. Ones I have seen advertised recently have been £3.5k + based solely on the fact that they are safe.