as much as you feel that you're providing value.
Too little with cause people to under-value your time, too much will deter people who don't have enough money for an expensive call.
Good luck and welcome to the platform.
Try to sync your total price to about a 30 minute call. It's actually hard for calls to run too much under 30 minutes so that's really your minimum threshold for taking time to answer someone. Don't worry about the per minute price, think more about a "per engagement" price.