It depends how well you want to live and where, really.
It is possible to find pretty decent accommodation for about 25,000 baht/month somewhere like Chon Buri or Pattaya, or for somewhat more in Bangkok or Phuket.
If you don't go to high end restaurants or drink much booze, you could get by reasonably well on 500-1000 baht/day. You could of course spend a lot more if you put your mind to it.
Leisure pursuits could get quite expensive depending on how often you want to pursue them. For example, a typical day's golfing would cost about 1000-1500 baht for green fees plus drinks and tips for the caddies (300 baht each usually). Plus a taxi to and from the course, obviously, probably another 1000 or so baht all in each way.
I know an ex-pat who lives in a rented apartment in a reasonably high-end condo in Pattaya. His overall living costs are about 100,000 baht per month but he plays golf three times a week and is out socialising for at least a while most evenings.