Of course it's not. You're free to set whatever price you want, but if you set that price and then try to explain it as "this is what it cost me to buy it", that second part undermines your first part.

Your employer, to the extent they want to agree to this, is renting space from you and you're citing and setting the price to buy it forever as justification. That undermines. Just name your price and see if they take it or counter.