Hi House,
MOO (my opinion only). The best trap shooters in the world including current American Olympians (Lance Bade, Kim Rhode - Atlanta '96 Gold, Ladies Doubles) and Michael Diamond (Australia, Atlanta '96 Gold, Trench) without exception use o/u's. Therefore, to compete at other than basic levels, you must have comparable equipment.
There is, however, a starting point. You don't need the best immediately, but, if he intends to shoot trap seriously, the o/u is the way to go. A used BMW or Mercedes, in good condition is probably a better buy, at the same price, than a new Suzuki. If he intends to stick to ATA then a single barrel will do the job. If he wants to shoot clays for fun then any shotgun will do.
As he want's to compete in ATA, I strongly recommend dedicate the o/u to the discipline of Trap. Buy a Trap Gun, not a sporter that closely resembles one. Chose carefully and try to get some advice on gunfit, this is more important than you would believe. The good news is that most people are suited by standard stocks. Encourage him to study the sport as well. You will save a lot of money in ammo, gun mods and equipment if you understand the sport better than the next guy.
If you live in Washington State or its environs, go see Chuck Dryke and have a lesson. The point is that one or two good sessions with a proper coach will save thousands of dollars in ammo over the years and he will actually shoot better.
Let him move on to ISSF competitions as soon as possible. You never know, an Olympian may be in the making. Its not as difficult or out of reach as you may think. Live the dream.
ENJOY SHOTGUNNING and try ISSF Olympic Trench.