Sutton Meadows is close by. They have 3 decent grass strips of 480m, which may be a bit tight in your C172 depending on your weight. Airfield information and PPR details can be found here at this link:
ABOUT CMC
I've got Mitchell's Farm and Kingfisher Bridge closer to Ely then Sutton Meadows on my chart, but haven't been to either and know nothing about them.