You can ride "english" in a western saddle. Or vice versa. I could ride dressage in western tack and a snaffle with a headstall made of baling twine. In fact, I used to practice my 2nd Level dressage tests on a western pleasure QH gelding with all of his western tack.
I'll go look around on Ebay
for some saddle, but I will agree that your budget is limiting. I personally just would hate to sacrifice quality and the comfort of my horse for price. What seat and tree size do you need?