Thank you! It doesn't take a lot of maintenance, mostly side income at this point. But I have put in a LOT of hours on it over the years. I will work on it in bursts, and take a few weeks and work on it 3-5 hours a day, and then not work on it at all for a while. I do need to keep the image library fresh, but that is pretty easy. To be honest, if I worked a bit more on it, I think it could do a lot better.
Yes, many options exist. The big one is Flippa which will take just about any project and allow you to list. There are others that are specific for large businesses (either have a listing price floor or a revenue floor) such as FE International and Empire Flippers. Another new one that is 0% commission is MicroAcquire. I follow the founder on Twitter and they seem to be doing quite a bit of volume.
I've personally sold projects on both Flippa and MicroAcquire and happy to chat about the pro's/con's of each.
You could try listing them here. May or may not favorably influence the price, in the same way private forum sales can sometimes go more interestingly than eBay et al.