You can also look for lesser combos. Lesser and Butter are so close to the same thing that many people (including me) believe they are the same morph. The Butter Pewter is going to be the most expensive, with three genes, but that would give you the most possible results. Have you tried looking on FaunaClassifieds or Kingsnake.com? The classifieds there are a pretty good indicator of market price. I'm seeing Lesser Bees for $400-500 and that's going to be your cheapest option. Just remember that price is often dependent on quality, and one of the only ways to make your animals stand out when you're trying to sell hatchlings is to have the best examples of the parents you can get. To breed quality you have to buy quality.