I pay £30 UK per hour for fortnightly singing lessons. Its worth every penny.
Originally I split the hour with Hammerite so we each got 30 minutes - but that was too short. When she backed off from lessons I took over the whole hour, and the rate of improvement accelerated very sharply.
An hour gives you time to warm up, consolidate techniques and learn something new - and have a bit of banter as well of course.

Kris