Ask HN: If you have project making 13kUSD passively, how to value and sell it?

I have a 3 years old app (freeyourmusic.com), that nets 13 500 USD a month. This is after all the costs, with almost no human interaction. There are ocasional bug fixes, but to grew revenue the main piority would be to focus on SEO and marketing.

I was recently thinking about selling it, but I have no idea where to look for buyer or how to value it.

The reason to sell? I want to put 100% focus on my other project that finally after years of work started getting traction and should be making 10x than this one in near future :)