I use the BJ's Wholesale Club travel section (works even if you don't have a BJ's membership). I also am a member of National Car Rental's Emerald Aisle. So I reserve a mid-size vehicle and can choose any vehicle on the lot for the price of a mid-size. We just returned from Orlando in May and were able to get a Town & Chrysler mini-van on the aisle.
I picked up the van on the 19th of May and drove it home to RI (returning it on the 26th) for a grand total of..... ready??? $68.xx. Yup. A one-way rental with a mini-van for a full week for less than $75!!!