Yep I've had commercial nurseries tell me the same thing. The reality is that they're actually fairly easy to graft. The hard part is waiting millenia for the darn things to grow and root out. From seed to 3 gallon is like 2 years :-(. From 3gal to 7gal is a bit quicker though.
The high demand for saps is just recent; I think it started around 2007. Before then, you could find grafted saps for quite a bargain. Just like with anything else, the market for fruit trees is pretty volatile, and popularity rises and falls (and then rises again :-). I'll bet folks like Harry remember when Ilamas were in high demand. Now, I can graft half dozen and have them last me for years before anybody buys them.
Ok, now I'm waiting on Silas Wood to pop up. Makoks on either side have jumped out of their wraps.
Will post pics like I said...as soon as Silas pops or flops.
Someone (who propagates and owns a nursery) once said sapodillas are expensive because of the difficulty involved in grafting them. I can't imagine this is the case. I just think they are in high demand, like atemoya. They are both very easy to graft.