Good luck on the cheap front if he's that flat and wide - you might find a synthetic to fit - I'd start with the Thorowgood cob. I work for Native Pony and obviously we specialise in fitting the wide loads- you might pick something up second hand and I'm hapy to advise, with pictures of the horse etc. Other options might include the H&C tree from Ideal and the Haflinger tree from GFS.
I don't think he's that wide, wife has a different opinion, I will post some pics tomorrow to see what people think.