How do I work out how much my domain is worth?

I have been contacted by a large startup enquiring as to whether I would be open to selling a domain I own.

I currently have a side project up on the site and, while I've not worked on it for a while, I had intended on picking work back up again and developing the project further. It wouldn't be the end of the world to rename the side project, however.

What I'm unsure of is how to work out what a reasonable price is for the domain. They have offered $1000, but I get the impression this is likely a low ball offer.

Is there some established way for finding out what similar kinds of domains would typically sell for? I do believe this one is particularly high quality if you're looking for a domain in the space.