My condo is ~$850/month. You can live cheaper or more expensive than depending on standard of accom and location. There is a twoplustwo'er that rents a place for about $200/month and likes it.
I can recommend this agency for condo rentals in Bangkok:
http://www.bangkokcondorentals.com/i...crt=2&Itemid=3
Internet ADSL is $40/month.
Air con can get expensive if you have it blasting 24/7. Budget around $100-250 per month for electricity depending on how much air-con uou use.
Meals, i spend $12-15 for a 3-4 course meal with drink for foreign food, less than half that if I go to some small restaurant and eat Thai food. All the good foreign restaurants and some good Thai ones too you can have delivered to your place by ChefsXP
http://www.chefsxp.com for zero markup between 10am and 10:30pm.
A ride on the sky train around 60 cents. A 20 minute taxi ride is a couple of bucks.
If you want to go out drinking and shipping girls every night you could spend a lot of money in Bangkok, but other than that it's hard to really spend a lot of cash.