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.
Such practice is omnipresent in America too. For example, the whole pet industry (Hills and Royal Canin), in America, make a fortune with deceiving marketing on their bag and can.
Also, if you are a repeat visa or visa exempt runner, you'll end up denied sooner rather then later especially since the new 60 days visa exempt which made most airport and border tougher. I got denied entry in Nong Khai after 10 years in Thailand (last December). So it took a very long time for me to get into trouble. I got in with an agent. You'll get in that way. You need to contact an agent and use fast track service to get in at Phuket airport for about 6-10k baht. It's basically a safe entry without hassle for people like you and me that will always moving forward be denied without a safe way in.
There is no such thing as a 180 days visa exemption time limit. I was in Thailand for 3000 days on mostly visa exempt before getting into trouble getting in :)
It's the wording. You can trust Thai Visa Centre. It's their job to know such things since they offer fast track and other services. It can be 1h before your flight if you want to. It's a TM6 equivalent, automated in their online system.