Not a big deal though, and I take your point about the oddness of the expensiveness.
From the guardian.co.uk
The ongoing expensiveness of this city is why it never disappears.
From the smh.com.au
The expensiveness of the building makes it a tougher challenge to find a new owner, Frank said.
From the dailyherald.com
Without meaningful documentation to justify claims of expensiveness, burdensomeness and public abuse of process, a piecemeal dissection has been advanced.
From the dailyherald.com
More examples
The quality of being high-priced
In business, retail, and accounting, a cost is the value of money that has been used up to produce something, and hence is not available for use anymore. In economics, a cost is an alternative that is given up as a result of a decision. ...
The state of being expensive; entailing great expense