While I'm not generally a fan of self-publishing, I would suggest that you look more seriously at it in this case. You'd get to keep a greater percentage of the profits, and since you have an established reader base, there's a strong possibility (possibly bordering on probability) that going with a small publisher won't sell any more copies than you'd sell on your own; or, to put it conversely, you could sell as many on your own as a small publisher would, and by self-publishing, you'd make more money.

Can I just say, though, that it could be worse? My publisher took books 3 and 4 of my series OOP, and I can't do diddly squat with them without having the rights reverted on books 1 and 2. Sigh.