Walmart offers the Camco 5.3-Gallon Travel Toilet for $48.33. Order via in-store pickup to drop the price to $45.04. (Amazon charges the same.) That's the lowest price we could find by $20. It features a bellows-type flush pump and measures 16.4" x 16.25" x 18.4"

Update: It's now sold out at Walmart; however, Amazon still offers it for $45.04 with free shipping for Prime members.