Rocks(off?), you might want to read this very long thread on tipping amounts: http://www.sawatdee-gay-thailand.com/fo ... light=tips
It's actually from the Old Sawatdee but was moved over here (somehow??), so it's rather not so well intact vis-a-vis "posts in order" ... the move must have been a bumpy ride. But you should be able to get the gist, as well as some good ideas on your original query.
Cheers ...