Why do you want to pay them so badly? In my considerable experience I've learned that ymmv is the king. You're mileage will increase greatly if you come across as a very nice guy who pays a bit above the asking (tip in advance so to speak, and if you come across as a sensitive, caring type who asks a lot of questions about the girl's life, what she likes, where she's from, her family, etc. The ymmv quotient is usually dependent on your age, looks, personality, and generosity. If you don't have age and looks then personality and generosity will go a long way. Try it.
But why Phuket bar girls. The real success is with the Philippine country farm girls or manila/Taguig slum girls. A dinner out and a little shopping trip to the mall, a stay in a nice hotel where she can shower and get herself made up and dressed up in the clothes you'll buy her and you'll have a submissive, insatiable honey that will do anything you ask. You might end up at her family's dinner table though, which can be kind of fun, but you should research the long term results that can have. For best results, post an ad on CL looking for a 'tour guide' and describe the situation in detail to make it clear you are looking for a girl to travel a bit with around the country and that will keep your bed warm at night, rent a car and book a few beach hotels, nipa huts are basic, cheap and beach fun. Get lots of groceries. Buy her some clothes, make up, mp3 player (if you have the means get her an iPod touch and she can video Skype you, she'll do anything for an iPod Touch), and a swim suit. Take her swimming and hiking, some other touristy type things. Make her dinner and open a nice bottle of an Alsacian sweet white wine. You'll find heaven and she won't care if you look like Jabba the Hut. For you it's like having the hottest girlfriend imaginable that just loves you to bits and for her it's like a holiday where she gets everything that she sees other people have but could never afford. This sounds expensive but if you add up the bills from Phuket you'll see it's quite a modest amount. If you fall in love then that's your business. Just remember to treat her like a princess and she'll treat you like a king.