you can get 1 year extension in country starting 45 days until 15 days before the date indicated on the last entry stamp. Obviously you must meet all the requirements such as TM30, 400k in a Thai bank and so on.
leave and return isn't a good choice now. Even if you have a 1 year multi entry visa such as those you get in HCMC or Savannakhet, it's better to extend it at your local immigration office.
I've never been asked to prove 10k. Just last time I was asked to pay 35USD for the Visa on Arrival because I was going to visit a customer. I was there just a few days before they started with border closures