Cost effective way of dividing up basement access for duplex

[Jay Chung]

Is there an easy way to divide the basement up? Each side of the duplex has access to the basement but below everything is connected together and I want to make sure no side has access to each other. The way I can imagine is perhaps putting up additional cinder blocks but that sounds expensive. I can put a wood panels but I don't 'know how long that would last.  I am at this point looking an easy/smart way to put something in between. The gap opening is roughly a 11 ft and 6 ft high. Thank you.