a1dookie,
It depends on how short or how long. 18 iches to 24 inches will break targets OK, but since you mentioned trap and skeet I would suggest longer. Most buget pumps come with a choice of 26 or 28 inches. I would choose 28, but would prefer 30 inches. There are very few 30 inch pumps available except for target models and older pumps like the wingmaster. You may wish to think about a barrel with choke tubes? More open for skeet and tighter for trap.
There will always be those who tell you to up the anti on an entry level gun. Since you say you are on a buget I will not suggest that. There is a lot of fun to be had breaking clay with a pump and one may satisfy your needs till you decide if busting clay is for you. Just go out there and have fun.