You are earning ~$60/day and that's quite an achievement to say the least considering there are tons of games on the App Store. A quick check on the App Store shows a pretty good rating of 4+ and I see there is a potential to keep this game going instead of selling it off.

Anyway, if you are really keen on selling it off you could try eBay or better still contact other iPhone/Pad game developers, companies to see if they are interested to buy it. As for price, I'm not really sure.

Good luck!