6 weeks for 3 girls? I am sure you can do much better than that.....like at least 6 girls one for each week.
Your best bet for model quality, guaranteed bonk at a reasonable price is to go to the MP at Ratchada - top on the list would be Poseidon (3rd floor), Emanuel and Mirage (model lounge). If you like the girl and wanting her to spend the next evening with you, you can talk / propose to pay her an acceptable amount, all depend on quality. Let say the girl work at model lounge at Poseidon at the 3.5K baht price range (not the very top end) but there are some gems; she would be getting about 1/2 or 2K baht per customer, one night she would be getting around 3 customer at 1 1/2 hr slot each, which allow her to earn around 6K baht. If you discuss and negotiate to pay her 6-8K for the night most will be happy to accept the offer, it less work for them and they get to go out and enjoy the night life and entertainment with you all paid for by you of course. Of course you could always try the one session and see if the girl like you enough to say stop work the next day to accompany you for the night without you having to pay
....in the end you would also likely be giving her some money.....by negotiating up front it clearer and usually make the girl happier.
There are gentlement club like Pesagus etc... where you can also take out the quality girl but price also can be quite expensive.
Escort services is expensive and the quality certainly varied; a bit of hit and miss sort of thing where the girl come to see you usually are no where as attractive as the photo you see when they send you or on the web and certainly price for the whole night would start from around 8K baht upward.
The MP option allowed you to try out one session at a marginal cost..to test out the girl services and quality and whether you click with her or not. it is very important that you do otherwise you be wasting money and not so enjoyable
Cheers