Do you mean like a foam latex groundbreaker, or something animated? If you are looking for a static prop, you should consider making them yourself. It's pretty easy and lots of fun. If you haven't seen these, check it out:
You're not too young to be able to build something like this... I was making crafty stuff before that age.
If you want to spend the money, then there are always the standbys like Spirit Halloween Store, Halloween Express, Fright Catalog, and the like. But you will be paying LOTS of money for a prop that isn't unique or even particularly well made (depending on manufacturer - since this sort of thing is a seasonal sale, they don't generally have good stuff for cheap).
I'm not sure if this groundbreaker is the best, but I'm fond of him. I bought him from Spirit last year for about $50 or $60 but I don't see him on their website anymore. I believe it was exclusive to Spirit.