Q: How do I sell things? Where's the market board?
A: Many, many things here, so I'm just going to suggest reading the Buying and Selling from the Player Market article on the main site.

Q: So how much do I sell this item for?
A: There's never an actual answer for this. Just like the RL economy, this will fluctuate. Feel free to discuss it, but please bear in mind that not everyone has the same views as you do!