I saw a K21 glider perform 22 consecutive loops straight from an aero-tow to 3000ft, and he still had over a thousand feet left
That would have been 22 loops under a large thumping thermal or in strong ridge lift.
A 3000' release in still air would normally restrict you to around 10 gently flown figures in a K21. Unless you want to land at the bottom of the last loop..
Having done both I would heartily recommend the OP sticks with the power route, it is ultimately cheaper and
much better for training because the tempo is more flexible and repeating figures is obvioulsy more feasible. A tow to 4000' costs £40-£50 and gives you 6-8 mins of actual aerobatic time - about double the cost of a Pitts S2A!
That said, a few power aero pilots have been know to experience the joy of soaring a Pilatus B4, throwing in the odd loop and roll between climbs!