I would not use ebay - their fees are high, and you will get bottom dollar.
Right now, a lot of people are trying to rent their timeshares, so you want to price your week competitively, market it well, and make sure you have a lot of traffic - because you have a lot of competition. If you really want to rent it, it's worth spending a few dollars to list it on several websites, so more people see your Ad.
I personally use these cheap or free websites to post my Ads:
TUG Timeshare Marketplace -
http://tug2.com/timesharemarketplace/
1 year Membership - $15
Ads - free up to 25
www.craigslist.org (free)
www.redweek.com
Membership - $14.99 for 12 months
Timeshare Rental Ads - $24.99/ea for 6 Months
Timeshare Resale Ads - $59.99/ea for 12 Months
www.myresortnetwork.com
Membership - free
Timeshare Rental Ads - $19.95 ($24.95 - floating weeks)
Timeshare Resale Ads - $34.95
There is also a list of resale websites at the top of the Buying, Selling, Renting, board that you may want to take a look at.
On Craigslist, you need to create a Craigslist Acct., and every 3 days, you can renew your Ads with the click of a button. You don't have to rewrite the Ads - if you create an Acct. they will be saved in your Acct. and you can just use the "renew" function, to renew the oldest Ad every 3 days, which will bring it to the top of the listings.
Good luck!