I spend every winter there and just returned from a two month stay. I concur on the price of some food items. To be fair, dining in a restaurant can be commensurate with US, and even Thai prices. But I'm partial to small towns and street stall dining. I live just 5 miles from the border and do a fair bit of commerce cross border so I'm not strictly a seasonal visitor. I'm well attuned to the exchange rate and day to day pricing.
I just returned from a two month stay on the Sea of Cortez. I never felt unwelcome in the town where I visit yearly. No issues at all crossing the border in either direction. As always one's demeanor, dress and language capability can make a difference.
The 180 day entry is not a "visa". It is, technically, an FM (Forma Migratoria MĂșltiple) which is essentially an entry permit. For stays longer that 180 one would apply for a Temporary Residency Visa. That visa has some rather high savings/income requirements but is valid for one year and requires no other "check-in". For what it's worth I have never been asked to show, at a traffic stop or at a border crossing, to show evidence of my FFM.
I live near a small Mexican border town. I travel to Mexico frequently through this town, often for weeks or months at a time. The only documentation I ever show is my driver's license and auto registration before I'm waived through. Upon my return I show my passport card. It gets scanned but there is no way US border patrol have any idea how long I've been in Mexico.
You're correct, but the METV permits the holder unlimited entries into Thailand for up to a period of 180 days in total with required exits every 60 days. Whether one extends one or more entries is immaterial.
For a bit of clarity, there is the SETV (Single Entry Tourist Visa) a e-visa issued for 60 days. There is also the METV (Multiple Entry Tourist Visa). Which allows up to 180 days stay. It appears the METV is what the OP obtained.