Glider with "respectable performance", rated for aerobatics, 300 lb pilot weight, and cheap? This is one of those pick any two moments :x)

300 lbs weight will rule out most single seat composite gliders I'm aware of, as most have an upper seat limit of 242 lbs, simply fitting in will be another issue, though broadness in hips or shoulders can further limit choices.

Compared to renting powered aircraft, renting gliders can be significantly less expensive. But as far as purchasing, I think you are not going to get into an aerobatics capable, decent performing glider, or powered aircraft, for $20K. Maybe a partnership or club with a Citabria and go for powered aerobatics?

"I'd pretty much like to soar, loop, spin and roll for fun while sharpening stick and rudder skills without an engine to worry about (cheap) . . ."

It won't be easy to find "cheap", but as to powered aerobatics, I wouldn't fret about the engine - - if it quits, you'll have the glider you wanted in the first place. Albeit, not such a high performance one.

good luck

bumper