I would not recommended eBay or Craig's List based on the many stories I have read from forum members on other photography boards. There are just too many scammers, and with the value of that lens, I would not chance it. MPB and KEH have reasonably good reputations as do many local camera stores, and you might even find a camera store that would consign it, but they will not give you what you could possibly get if you sold it on your own. Fred Miranda has a reasonable reputation. If you lived in a reasonably populated area, you could see if a board member from here or other reputable forums where you are a member might be interested. Then again, since you bought the lens used, you could break even depending on its condition and if you have all of the boxes and materials originally included.
Good luck,
--Ken
P.S. And most importantly, best of luck with the RA!