You can buy little ponies at many sales for about £40. Expect them to have been badly weaned, full of worms, unhandled and probably with some virus or another though
At Holmfirth last week NF colts were going through the ring at 40 guineas. Older welsh ponies which appeared to be ok (didn't look closely 'cos I wasn't buying) were fetching 350 guineas. i think if you are looking for a made pony £150 is very optimistic but if you want to put the work in you can certainly pick youngsters up for not much more than pennies. Your best bet is probably to PM JM.