cheap is something you probably won't find in a new pant that works well. Try the trading post though and see what is for sale there. If you aren't worried about them being waterproof (even though they say they are, we never found that to be true) .. we liked the bumpy trainers for $12.50 or so. They DO leak with a full pee, but they keep pee from dripping down the leg and onto carpet. Just don't expect them to hold a pee under clothes and keep clothes dry. They fit really nicely though and are soft and cute. The other cheaper ones on the market are bummis. We had a size too big and the legs were still WAY too tight (and my daughter is thin) and the rest of the pant was POOOFFFFYYY.. and they leaked.
Sorry I'm not much help. Most trainers that work well are kind of pricey. We tried a ton of them. My personal experience is this.. trainers at home were counter productive. She started using them as a diaper. So, we went to panties at home so she could "suffer" the natural consequences and understand why it's necessary to sit on the potty. And I had nice trainers for going out. the only pants we trusted out of the house were potty dance pants. you can get them at bum-ware.com
If we used trainers at all around the house for everyday wear, she very quickly regressed to not wanting to use the potty. So, one or two pair got us by just fine for the occational outing.