"Good Guys" used to be my most expensive but of course it came with the membership.
"Classic Bike" used to be expensive but for several years it's been a standard Christmas gift from my wife. Even when I paid for it it mattered not and I'd have paid twice as much for half the issues. I don't recall any magazine for any subject which gets more worn out and re-read by me. Currently, in fact, in my meditation-station, fortress of solitude and otherwise, well plumbed and ventilated "safe room", I have a 2011 copy which has a great article advancing the notion that a Le Mans takes no back seat to a Ducati 900SS.

Now though, my most expensive is "Garden & Gun". Fine publication, that.
Todd.