The ground isn't in the town centre, but there is a nearby train station (St. James' Park) so what I'd do is park in a place called Polesloe Bridge or Topsham(sp) and get the train the one or two stops, you'll probably be able to find a place in one of the estates for free or alternatively park in town and get the train down. I think most of Exeter's resedental areas are free to park but not near the ground (same as SMS) but if you drive around with in 20 minute walk you'll find somewhere eventually if you want your car nearby, but its a nightmare to get out of the TC.
(P.S still looking for one ticket )