My horse has a dipped back (typical of welsh cobs) he also has highish withers huge shoulders and a short back. So Im considering a treeless to avoid fitting problems. Are these competions legal?

If not are there any alternatives that will not cost an arm and a leg?

As long as it's a western style saddle with horn & fenders etc there is nothing to stop you competing on a treeless.
You could also try getting a saddle fitter that either fits custom saddles or has a wide range of saddles to fit one for you - try either Don Fechner at the Western Boots and Saddle co. or Jennine March at March Horse and Tack.
Another option may be to get a built up saddle pad.
Hope that helps!!!

I rode in a western tressless ofr ages, as long as it has swells and a horn its legal for WES Im not sure AQHA accept them?
Treesless is good but with the one i had, a Barefoot, i found i coudlnt use my weight so well, but other styles are more expensive bu dont have this problem. they have altered the barefoot since then though and i dont think they will have this problem anymore, they dont look the nicest of saddles on though, try the bob marshal they are a little more expensive but look nicer.

if your nto in a hurry though, when my mare is sold, if she doesnt go with ehr saddle it will be for sale, it is a very very nice saddle and is for an incredibly wide horse, extra full bars, but accomodates a horse with a wither