I am not familiar with a Sumner brand, but I assume you've priced hypalon inflatables from $800 to A BUNCH, depending on size and features.
That said, if a Sumner is "incredibly cheap" it is probably made of PVC.
If so, Here's my opinion:
I owned a PVC made by Sevylor for 6 years and never had a problem, but it was babied and well cared for, i.e. not allowed to hit pilings or sea walls, stored indoors when not in use, cleaned with mild soap, never left in the sun for days, etc.
I now own a hypalon that has lasted 8 years so far, but it has been through the 'rebuild' treatment (valves replaced, floor seams re-glued - cost of $250) at the authorized repair shop.
If you are careful, a PVC dinghy could work.