String lights hanging for an outdoor patio: very summer camp and warm, but isn't it costly to have on?

I'm currently in a situation where I want to buy string lights to hang outside on the patio but worry about the added costs in my electric bill due to the number of bulbs being added to the overall lights in my single bedroom apartment.

Does anyone here have any experience with string lighting and its added costs towards your monthly electric bill. As an added tidbit of information, I want string lights because I plan to invite women over for some great talks and equally as great love making.