Is the 5-year DTV visa for 30,000 Baht legitimate or a scam?

The 5 years DTV is 100-125k baht with agent (if you don't have the proof of 500k for months in your account). It's the current on-going cost with most agent using their contact in Vietnam. 30k would be a scam, yes.

I think it's better for you just to continue with the retirement visa, the DTV also has a ฿500k financial requirement, and you would need to pay for a soft power course, such as muay Thai or cooking classes, and every 180 days you would need to leave the country, or do an 180 day extension which is not easy to do, and can only do it once, I personally don't think the DTV is worth the hassle if you can do the retirement visa, the DTV is apparently becoming more and more under scrutiny.

Hanoi for DTV I'm told

On your computer you say

It's the DTV. It actually costs 10,000 baht if you do it yourself. And while it's valid for 5 years, you can't just stay in Thailand like you would with a retirement visa. You'd pretty much need to leave every 180 days and then come back for a new 180 day stamp. There's also no guarantee that in the future they won't start asking you for proof that you're still doing what you initially said you were doing to qualify for the visa. Many embassies have started tightening up the requirements and immigration might start too at some point.

The retirement visa/extensions will give you a much more secure ability to stay in Thailand.