Hi jinx!
I wouldn't think 4 bags and 2 duffles would be a problem for the Budget van to the rental office. We had a very, very large suitcase, a smaller suitcase, and a very large duffle and we still had room for another family of 4 plus their bags. We had packed a bit more than needed, since we had been at WDW for four days prior to the cruise.
The van is about the size of the Mears vans and can seat about 7 or 8, I think. Behind us in line was a family of 5 with about 7 pieces of luggage-- the van that came right after ours picked them up together without a problem. Budget had two vans running that morning.
Hope that helps!