If you don't own an airplane capable of aerobatics flight or there isn't an nearby FBO with an aerobatic airplane for rent, sharing an airplane through "co-ownership" may be an affordable option.
An arrangement in which several pilots "co-own" an airplane or form a Limited Liability Company (LLC) that buys an airplane that the LLC members can fly can be an affordable option to sole ownership when renting an airplane isn't an option.
AOPA has webinars covering the advantages and risks of forming a flying club (insurance implications), co-ownership agreements, and LLCs.
Chapter 67 has two groups of pilots who formed LLCs to buy Super Decathlons for recreational aerobatics and contest participation. Contact email@example.com for a copy of a Sport Aerobatics article series describing their experiences.
Often in a group whose members share ownership in an airplane there's a member considering offering to sell his share, so don't be discouraged if no LLC or co-owner membership shares seem to be publicly "on the market". Contact Chapter 67, who may be able to introduce you to a member thinking of selling his share. You'll find that members of these groups are happy to talk about the lessons they learned in joining or forming a group.
For people who satisfy the membership criteria, the Boeing Employees Flying Association (BEFA) includes in its fleet a Super Decathlon . BEFA offers aerobatic instruction for its members, several of whom fly in contests
AOPA conducted a three-part webinar on co-ownership and forming an LLC for sharing the ownership and operation of an airplane.
Read a short AOPA article about co-ownership here.
These SuperDs are owned by the LLCs described above:
Several Chapter 67 members own shares of this Christen Eagle, preparing in this picture to fly in a contest at Ephrata Airport.