I have a belly boat, two pontoon boats (both of them purchased used) and a dinghy type boat for 3 people. Don't get the wrong message here, financially I am far from being well off (live in a townhouse with no garage) my go to pontoon stays inflated in a garden shed in the 20 x 15 ft backyard I have, and yes I do have a truck to haul it around with. My suggestion is to wait for the right (used) boat at the right price. I have always thought that going cheap in the long run will end up costing more. A top end pontoon will last forever (1 of mine is 20 plus years old and still going strong). Yes they are pricey, but buying a "disposable" boat might be something you might regret as they are not as sturdy and safety is a must. Cheap boats are cheaply made, with cheap materials, cheap labor etc. The last thing you want is to hear is a weld cracking while in the middle of a lake or floating a river. I have no regrets with my purchases, they were not cheap, but I know I bought what felt was the right thing for me, as I feel safe with any of my boats
If you must have a pontoon for a trip, rent or borrow until you find something you can afford that will suit your needs.
Belly boats do have their place, for myself however I have not used mine in over 6 years, if I ever need one, it is sitting there waiting for its time to shine.
Oh yeah, I am contemplating buying another boat, one with a standing platform, but we'll have to see how that goes.