Agoda website
Review score 8+
Chiang Mai 302 hits < 510 baht
Khon Kaen 9 hits < 550 baht
Pattaya 109 hits < 630 baht
Phuket 155 hits < 500 baht
Based on this Chiang Mai is cheapest, KK is most expensive!
Not sure it is poor. I saw plenty of nice cars and well dressed people. Nong Khai is a nicer town but I wonder if Ubon would be better for an allrounder.
Food is very cheap in Phuket away from beaches. Transport is high. I don't know about bars.
Chiang Mai and Pattaya have Bolt so cheapest transport. Also lots of cheap rooms.
Nakhon Si Thammarat is more interesting than Khon Kaen.
For cheapest good room near beach Lanta wins but bad food.
I found the town hotels 200 baht more than other towns. Phuket has cheaper hotels. The averages are distorted by high end resorts. The best value hotels for price and quality under 1000 baht is Lanta.