Really depends on the studio and the country you live in.
Greece one group lesson a week for a month cost about 20 euros. Doing three a week, as many studios offer, cost on average 50 euros a month.
Private lessons seem to range from 20-40 euros per 50 min lesson (thats 25-50 US$)
But that depends on how well established a studio is and what they offer. An old, established studio that just put in a state of the art floor will ask more than a new studio that needs students.
Someone new to dancing might be gieven higher rates than someone more experienced (especially male dancers seem to be able to bargain quite a bit if the studio in question is lacking gentlemen for their group lessons and parties).
You'll have to shop around. Look at what is close to were you live, which space feels best and who you seem to get along with best. Most studios do a free sample lesson, try them out.
Do NOT choose a studio just because the instructor is gorgeous
