There is no such thing as good and cheap in BKK. I know of a few locals only massage joints but u dun speak thai so kinda hard for you so i will recommend you my fav, a place where i will always go with my clients.
HealthLand:
http://www.healthlandspa.com/location.html
its a little more expensive than other places but once u tried this place, u will never go anywhere else. When your comparing to Sin then its still considered cheap ! About 6000-12000 baht per session !