Get married in Thailand and apply for extensions based on marriage. That's by far the cheapest way. You just need ฿400k in a thai bank account instead of ฿800k as a retiree. Don't even think about an Elite visa. The cheapest 5 year option cost ฿900k. You don't need to use an agent.
He couldn't use his marriage license because it wasn't valid anymore. Meaning applying for a 1 year extension based on marriage isn't possible. He has to go for the retirement option instead.
It's the TM87 form if you arrive on a 30 days visa exempt and want to convert to a 90 days Non-immigrant O Visa based on retirement. Then after ~60 days you can apply for a 1 year extension based on retirement. You must do this in the province where you're supposed to stay=your permanent address. That's the immigration office where you belong,so to speak. The O-A Visa is only issued back home at an embassy or consulate. Don't ever go for that. You can always go to an agent in the province where you're staying. The price will most likely be much less than ฿22k because you meet the financial requirements.฿15k should be enough.