How much can I ask for my travel system on craigslist?

I paid around $280 for it brand new. It is a Chicco Keyfit 30 in green and brown. I just bought it 3 months ago, the car seat doesn't expire until Dec. 2016 and I only used the stroller maybe 5 times. I decided to upgrade myself to a Peg Perego. What's a fair price?