If yo have insurance, You can keep getting O-A visas every two years. No need to keep money in the bank. A single O-A visa will work for two years of stay in Thailand with one exit/entry. However you may have to time your insurance accordingly.
A second of option to avoid keeping money in a Thai bank is to hire an agent for yearly extension. The first year, it will cost you around 30K and subsequent year, it will be 15K (Pattaya rate). With an O-A visa, you will have to ay 15K for yearly extension with agents in Pattaya.