This notion that a girlfriend costs more than a SP is rediculous. It is not like the guys who see SPs are hiding in a hole the other 99% of their lives when not seeing the SP, and in that 99% of time they are spending allmost as much money as they would in a relationship (possibly even more if they are into the party lifestyle). Guys on PERB like to say that because it lets them rationalize their activities, but truth is they are simply not being honest with themselves.
For most clients visits to SPs account for a few hours a month at most, few people with regular jobs could afford more. Compare that with the 100+ hours a month you would spend with a girlfriend in a relationship, and it is clear where the value lies (if you like to account for those sorts of things in life that way).
I don't doubt that there are a few women out there who demand much more, but the overwhelming majority of normal women don't require the kind of massive investment that some of you guys seem to think. If it turns out that most of the women you get involved with do require that sort of maintenance, maybe you need to re-examine the sorts of women you are pursueing and why.