"Offroading vehicles are expensive" and "Offroading vehicles is expensive" are both grammatically and factually correct statements.
It can however be big fun if you do it right...
I've decided that if I ever get back into that, it'll be with a reliable knockabout vehicle, and I'll learn to be happy with what it can reasonably do. Maximalism is what runs up the tab, especially if the vehicle also has to serve as a nice daily driver (which can also wet-blanket the off-roading if I start thinking too much about breaking stuff...).