You can find good/vgood condition Remington 1187's for 600 ish.
You will not find a better do it all gun for the money that will hold up to cycling the gross amount of rounds used in clays trap skeet and hunting.
do not get a pump. it takes the enjoyment out of the game. period.
I still use my 1187 for single trap and over 6 years it has very rarely FTF a round.
When I graduated to being a total clay addict, I tried a lot of O/U's and found the Browning Cynergy to be superior to the typical Citori that I had been shooting. Citori is long since sold and I do not miss it one bit.
Beretta's 686 series is also a great clays gun. If the Cynergy did not exist, I would be shooting one of those.
The first rule of shotgunning is find a shotgun that FITS YOU PROPERLY. If a shotgun fits (as it is a pointed and swung rather than aimed at a target) you will break more clays and love the sport and gun.
A poorly fitting or fiddly gun will take all the enjoyment out of the sport. I have seen guys with very spendy guns get whipped by people with lesser arms simply because the gun does not fit them.
Length of Pull is the first fitment to make.
Receiver height is the second.
Balance point and hold is the third.
Patterning is the 4th.
Once you get all 4 points working in harmony, it's damn near telepathic when shooting. And it should be. Instinctive, point, shoot, kill. And you need all 4 of those fit issues to be right in order for that to happen as naturally as possible.
Barrell Length: 26-28" for skeet and open chokes. 28-30 for 5 stand and sporting clays (choke selection based on target presentation) 30-32" for trap (choke selection based on skill and load weight of shot and handicap) Personally, I find 30" to be the best overall compromise to do it all, and then make up for distance (short or long) with choke tube selection.
Best of luck.
PS if you do get a gun like that, be prepared to eat a lot of top ramen. The game gets so addicting.... you will sacrifice a lot to keep shooting. Like taking 2 ply toilet paper rolls and splitting them to make 2 rolls... eating top ramen, loading down to 1 oz shot, reusing hulls with the crimp damn near blown off, etc.
When the gun fits, and the smoke rolls, there is nothing better.
With all due respect to IPSC, IPDA, F Class Shooting, and even gopher hunting, there is NOTHING that comes close to the fun of SMOKING CLAYS!
Seriously.