There are lot's of sensible answers and advice on here. The bottom line is what do YOU want. What are YOUR needs to enjoy a happy and comfortable day to day and what can you afford?
Either way however much you spend there are things you are going to love and things that are really going to get on your tits eventually - the more you spend the more you can insulate yourself from the irrational quirks of Thailand.
I've lived in Thailand twice (although never in Pattaya) and been visiting Thailand from the mid 80's until present day.
The first time I lived here was in CM and even then I was spending 8k baht per month on a 45sq mtr condo with a kitchenette type arrangement - 17 years ago. I allowed myself 20,000 baht per month spends including rent because I wasn't working. I bought a motorbike which was the best 25k baht I ever spent. At the time that was adequate and I really had a blast. I ate Thai food a lot and didn't cook at home much. From memory a bottle of Vodka in a bar was 700 baht with mixers - I think I probably still have a few stashed in bars up there
Then I moved to Bangkok the second time for a very well paid corporate job in 2011. $20,000 USD per month - I was grinning ear to ear for the entire 5 years! That kind of salary allows you lot's of choices and you can really have any kind of lifestyle you want. I am aware I was fortunate.
So, the second time around I decided that I wanted more space of the kind I would be used to in the west. Even so I only spent 35k baht on a 150 sq mtr condo with a separate, full kitchen. Full cable tv packages, maid (pennies), driver (slightly more pennies), lots of nice meals, girls/ladyboys, internet... it soon adds up. Even so, I found that around 150k per month was more than sufficient for a relatively opulent lifestyle. That, at the time, was $5k USD or £3k. You can't get anywhere near that kind of luxury in the states or the UK for that kind of money.
Anyway I'm blathering on but I think as others have said that 100k baht is a good number to set as a budget - if you can. Maybe most months you won't hit it but there will be times when the unforeseen happens - sick relative/friend, road accident, emergency trip home or other as yet hidden event - like running over a motorbike taxi driver... true story - or maybe a holiday away from it all - because I guarantee you that what is fresh and new will become irritating at some point. Can you live on 50k? Probably. Do you really want to? Only you can answer that.
my 2 cents