Many consultations are free, if he didn't mention anything and you never agreed to anything then you don't owe him a dime, at least not that anyone can get you to pay.
Do you feel as though you owe him what hes charging though? From an ethical standpoint, do you owe him for his time, or put another way, did you steal his time? He obviously benefitted by the free advertising for his services, since you rang him up for a consultation with the presumption he'd be on the case if it was agreeable. So even assuming that you got value out of the interaction, so did he.
Anyways I wouldn't pay him a dime, people really should be upfront with their prices and if they aren't, they could at least answer directly when someone asks. Otherwise they're just trying to trap them into paying.