Just a bit of info from a trap shooter, the reason that guns that are used for trap, skeet and sporting clays are so high priced is that they are built to be able to shoot hundreds of rounds in a short period of time, or even a few hundred-thousand rounds in its lifetime. Field guns, be they auto-loaders or O/U are not designed to handle that kind of repetition. A clay shooter can go through a few thousand rounds in a weekend competition while a dove hunter may only shoot a few boxes at best.There are guns designed for each of the specific sports as well. A trap gun is different than a sporting clay or skeet gun. Some people shoot a O/U because they can have a different choke tube in each barrel depending on how far the target is. In trap when you shoot doubles, the second bird needs a tighter choke.
Go to a registered shoot and there are normally vendors with tables and tables full of used and new guns for that sport (although there's been fewer and fewer showing up lately). It's the only time I get to hold a $50,000 Perazzi or Krieghoff, and think, "gee, I can miss just as easily with this as I can with mine, but mine costs a heck of a lot less"... You can get a decent gun for sporting clays for under $2000, but be sure it is not a field gun. A Citori is a good low-cost option.