The days of the 10-15K Avid/Foxes are over for now! When I started (yes, they had airplanes back then) it was $50 per horsepower and $5K per seat. Now its over $200 per horsepower and almost $20K a seat.
Might take a little bit to find one. A full swivel one like the RV series and several others is easy to make and requires less modifications and weight. It can be built into the engine mount fairly easy. A little backyard engineering and a few materials and you have it. Diff braking is a must.
Weighed mine today, minus engine and prop. Came in at 164 lbs, including engine mount and inst panel. Leaves me 90 lbs for engine and prop. The Hirth F-23 supposed to weigh 74 lbs with redrive and exhaust so it will be close or a couple pounds over the 254 limit. But around here the FAA isn't hiding in the bushes and I fly out of a hayfield.