You can create a bounty, but money generally isn’t a motivating factor for openHAB developers.
If you do go that route, you might want to consider that $25 isn’t much of a payout for a developer. I know you’re just throwing it out there as a starting point, but it’s less than two hours at minimum wage, or a neighbourhood kid mowing your lawn once or twice (I don’t know how much teenagers charge these days).
Even if you find 10 people to chip in, that’s only $250 for what will be many hours of work to code, test and debug. At least half of that money will go to the developer buying a Honeywell thermostat, and no one’s going to pay them for future updates or user support in the community. Which is why money typically isn’t a motivating factor for this sort of thing.
What you’re really looking for is a developer who’s already thinking about upgrading their thermostat. Then you can incentivize them to choose a Honeywell and develop a binding, perhaps by offering to buy a device for them and pay them for their initial work. Then it’s less about paying someone $25 and more about mutual benefit and collaboration.