Not that I even bother to enter a lot, but maybe you could work out “e-gift cards/discounts” with some site sponsors for a few $ off an order or something.

Not sure how difficult it would be for the sponsor to setup, though. Sort of a % for all GOC, and 2-3x% for just a few winners. Conditional on 3-7 days to be used. Maybe just a bogus stock item for winners to put in cart to show they won. Sponsor can control it as inventory and/or colour options maybe. 15 pvc pipes, ten in “hot pink”, 5 in “uranium-235”. And priced as more than anyone would pay to eliminate accidentally having wrong people try to but it.

It’d boost traffic to the sponsors site as hopefuls shop in advance and should drive at least a few impulse buys before and definitely after. Something that’s less work for both you and the sponsor. I realize even the sponsors have a shoestring budget and it’s typically more a labour of love than absolute profit for most.