eBay *is* a great place to sell an instrument but making that your first sale might not be the best move. You'll have to pack the instrument well and ship it... then hope the buyer doesn't decide to send it back minus a few parts.

You're better off using craigslist and insisting on local pickup with a cash transaction.

Even less hassle is to take that rig to your local music store and put it on consignment. They'll sell it for whatever you ask and keep around twenty percent as their commission. You don't have to show it to a million time-wasting tire kickers or be cased by someone who wants to show up and rob you.

A good way to find out what your used gear is worth is to see what others are selling it for on eBay. Or go with the "half of what you paid for it" formula. Maybe a bit more if it's still in mint condition. Yeah thats a big loss, but used is used even if its used for only a month.

Good luck.