I did a few solo 1 week trips a few years ago. I never negotiated any pricing and just asked the girl if they would like to hang out or have dinner before, after work or on their days off. I got lucky a few times and the cost was minimal for me the girls never asked for any money but I usually slip them something, ranging from 1000 and up for 1 over night or gifts in exchange That is not including food expense and gifts. (But it would depend how many days she spends with you).
I even went with a couple of girls on their day off to do visa runs in Zhu Hai a few times and usually spend 2 days and nights with them. Do a search on a few of my reports.
Another alternative is to head into Zhu Hai as it is so close and do some cheap shopping, Cheap KTV fun, and some less expensive saunas, mind you the saunas aren't as nice as Macau but if you're lucky gems can be found, or try to pick up civies in Zhu Hai I found it to be rather easy I got asked out a few times by the girls to go out, 1 was a girl who did facials in veggie massage place, and another was a veggie footie girl, both girls were very doable especially the facial girl who even offer to buy me dinner !!
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but i had plans meeting up with a sauna girl from Macau that trip.
Hope this helps, goodluck punting
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