How much should I spend on a male chastity device?

A custom cage can be hundreds of dollars or a cheap one can be found for under ten dollars. I typically recommend that you start with the inexpensive cages to figure out what you like. If this turns into a long term thing for you and your partner then you can look at spending more money. If you were new to skiing, I would suggest that you buy/rent cheap skis at first to see if skiing is right for you and then buy more expensive skis when you decide to go pro.