There's always potential but it's not going to be cheap. Out of drunkenness, I asked several girls how much to take her home after the lapdance. I got quoted $500-$1000 from some girls. Other girls said they aren't hookers. It depends on who's the girl. Of the times I did find success, I got it towards the mid to end of the night, when the girls felt like they either need to earn some more cash or they just hit it off well with me.
*Edit* oops I thought you said Viet bar. Nvm, I didn't have success with the cafe girls, but with the bar girls