Expensive is subjective.
For a japanese, who pays over the odds at home, fucking in BKK is like unbelievably cheap for them.
For a Singaporean, if you are used to paying 15 bucks to fuck in the forest of woodlands, then BKK is expensive
In my opinion, don't make fucking girls the only main reason for visiting Bangkok. Afterall, Bangkok has much more to offer than fucking girls. I mean how long can you fuck in one session. I still enjoy Bangkok, I visit Bangkok for holidays even if I go to Bangkok at least 5 times a year for business. To me its a very well balanced city, good food, nice cafes, nice people, very well connected public transport, plenty of options for different kinds of activities, reasonably affordable even with its rising prices.
Just came back on Sunday, 3 nights in Pattaya and 4 nights in BKK, fuck 7 nights in a row, but I also enjoyed visiting the usual tourist spots like Sanctuary of Truth, watching the Ah Gua shows all over again haha...