Title text: I've looked into this, and I can't figure out a way to do it cheaply. And I guess it wouldn't be sanitary.
Randall is playing with the child/grownup setup again. As we all know, our parents are defining our adulthood. Many of times, they do that by saying "That's only for grownups" (for instance, while taking controlled substances like alcohol, or smoking). At other times, you (as a child) get to hear "We don't do that anymore, we're grownups now" (for instance, playing at a playground). Megan has taken these thoughts seriously, and now she has defined her adulthood by creating a playpen in her apartment, going against the latter statement. Cueball also finds this definition great, as he comes into the playpen, and (I suppose) adulthood and childhood melt together, judging by the love heart.
The Image Text reveals that Randall also would like to own his playpen, but he finds it expensive to buy, and also hard to keep clean. Which is a fact. Most public playpens contain over 100 different samples of urine, as many children play in them, among which many toddlers. If you go to the local ball pit and count how many diapers you find at the bottom...you will be disturbed....until you find out that some of the black stuff down there did not have a diaper source.
Randall, author of the comic, actually built one in his apartment, which he talks about and shows pictures of at here and here. Speaking of cost,  has a calculator for how much it would cost to make your own ball pit. Looks like I need $4000 to fill my bedroom 3 ft deep.add a comment! ⋅ refresh comments!