How much do voice lessons generally cost?

I've already increased my range by nearly an entire octave just by using tips from my vocals teacher at school, but vocals isn't the same as private voice lessons so I'm thinking i might take them over the summer so I can sing with the higher sopranos instead of the mezzo sopranos next year in vocals. Cuz, while I can hit fairly high notes, they don't sound quite as good as i feel they could and i voice lessons could really help me improve the sound of my voice. So...just on average, about how much would this cost?? Just for the summer.