1. Money. 2. Leads. 3. Education. If you're saying margin is an issue, you should skew to the side of education and lead funnel model. At the end of the day, most good partners will always go with the vendors that are going to make them the most money. You should be rewarding the most loyal with actual money if possible. Otherwise, be strategic with who you partner with so you can potentially offer their services to your clients. Your partners will see quality customers as more valuable than reseller / affiliate funds. A lot of companies see this as a distraction, so you have to prioritize your bandwidth as such. From an education perspective, I see marketing swaps / partnerships as easy points of entry. This can be done through webinars, lunch and learns, blog posts, etc. It educates both the partner and potential customer bases. It really depends on what the company's margin is and their ability to actually "expand".

If its Company B's customers that can potentially win the trip, then Company B should pay more of the bill. That being said, who is receiving more value? If Company A is receiving more value by offering a trip to Company B's customers, then Company A should pay more. Another route you could take is with prize insurance. Create a competition where potentially no one wins - Ex. a hole in one during a company golf tournament. You pay a few hundred dollars and potentially someone can win a car. However, I think the answer to this question is based on who is receiving the most value. It doesn't matter if they are just email addresses.