Sounds like he fits the alternate definition of bisexual: anything he wants sexual he has to buy. Hey, it's a problem people have from time to time, ya know.
It really does raise the issue though, that like most of the rest of life the vast majority of sex is bought. No? Think about it: your house that you get laid in, your car that you used (or train or plane ticket) to get to where you met them, your clothes which although are taken off were most likely present and noticed before they were taken off (unless you picked up someone at a nude beach), the food you ate beforehand to have the energy for it, the gym you worked out in to get into any kind of shape to be suitable for anyone that you'd consider worth with, the condom(s) you used (I know for me and hope for the rest of you), etc. all were bought or the sex wouldn't have happened. You buy the opportunity. Sad, I know, but realistic. If you don't spend money in some way or form you don't get sex.