We don't do a lot of comps, 2 maybe 3 a year. Traveling is hard, teammates have families etc.
But we are sponsored by our local butcher. And yes. It is a 2 way street. He gives us all we need meat wise for the comp, even kicks in some sides and some incidentals to cook and hand out on saturday when people are walking around being nosey. In return occasionally I cook for his store. Which works well for me, it gives me exposure for catering jobs, he sells the meat, I do the cooking and we both make a profit and I don't have to carry my own insurance, food handlers certificate, etc. .
It opened up a lot of work for me, any BBQ that someone comes in and wants done, he gives it right to me. I spend the money on the charcoal, I make the rub at the butcher. On top of sponsoring us, the semi weekly cooking gig has worked out to a barter system. I'm a local celebrity now, and don't have to pay for dinner when I want a nice steak or something else.
This year we also picked up an egg dealer who is lending us an egg to cook on and giving us all the charcoal and smoke wood we need. In return, all she wants is additional exposure for her store. Really, monetarily all she's laying out is for the cost of her transportation of the egg and a few bags of charcoal at most.
It's a very expensive hobby, even if you only do it a few times a year. I would never expect someone to fund the entrance fee. If our team wins, whoever helps cook that weekend, after our costs are covered, splits the pot. If a sponsor gave us the entrance fee and money for incidentals i'd feel obligated to hand over at least some of the winnings.