Inexpensive way to section off unfinished basement?

eastie

We have an unfinished basement (concrete floor, no interior walls, exposed beams) and need to section off an area at the bottom of the stairs leading to the first floor to create a small 10' x 5' vestibule (reason: we want to put a litter box down there and don't want the cats exploring the rest of our filthy basement). The stairs run down an exterior wall, that wall intersects with the back wall so we would only need to enclose the other two sides to section this part off:

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I'm ready to just go ahead and frame this thing out and throw up drywall and a door, but are there any other options we should consider? Take into account that this is likely temporary anyway; we have in mind finishing this space in the next 4-6 years, so whatever goes in here would just be torn out. No need for any insulation, sound deadening, etc. Just needs to be a cat barrier. And, yes, those suckers can jump high! If we do frame it out I am going to probably put in accordian doors or a large sliding door on the long side to make moving stuff from the basement to the 1st floor easier (with a standard door opening that turn would be a little tight for larger objects). Thanks!