It's almost double the price of the dealers down the street (not that i would know...) Some believe it is safer than going out in the real world and dealing with shady people. TOR with a VPN and pretty secure, but getting packages has never been. It's a numbers game, the more you order, the higher chance of getting caught. Although there are ways around the package problems, they just take time and money.
It probably is more expensive if you are buying small quantities but I think the advantage with bitcoin is that you can buy it in bulk and bulk purchases are always cheaper. You have a great point though that there should be some premium for the safety you get with anon orders using TOR.