closing up cinderblock foundation- how would you address?

[Jeff Bridges]

I have a rental property that I will be doing some energy efficiency improvements using local utility grant money through the energy star home performance program. I will be encapsulating my cinderblock foundation with poly and spray foam using professional vendor. I found out in order to complete, I need to fill in the void underneath the entry stairs so they can spray foam the foundation walls all the way around. that is the only place where cinder blocks are missing. Do I a) fill in with 9-10 cinder blocks or b) use cement board and just paint the cement board (probbaly the less expensive route. Its going to cost me around $900 to do it the right way with cinderblock, but I just want to make sure I havent missed another option that wont look bad when I go to sell. There is already an access hatch for the crawl space in the corner of the property so I have another primary access panel for crawlspace. Thanks for your feedback!