I think the last thought in your post would be the best way to approach the brewery to make some sort of financial agreement if they are interested. Sell it to them as the beer that could change their bottom line, and because this is a recipe that you have perfected over the last year or two if they have an interest in your recipe that you are looking for an offer.
You are already formulating for them, albeit they are paying for it (which is pretty cool), to offer a recipe that will eventually become the brewery's, so if they choose to make a deal they should provide you with some sort of royalty or a recipe buyout. Bear in mind though, a good brewer can take your beer, and make a close version, and tweak it themselves to their liking, producing a beer that may be extremely similar to the beer in question.