I'm not going to invite my husbands extended family to our wedding
Why don't you want them there?
I don't want to spend that much money.
That's understandable, because weddings are quite expensive. It's fine to not invite his extended family, especially if you don't see them very much. You should check with him before making any decision, though.
I guess but they will just suck up my money and they are going to treat my husband and I like shit.
If they don't treat you or your husband well, then it's fine to not invite them. You and your husband shouldn't spend money on people that you don't want to be there.