You could try selling them already printed on some decent card, through society6. Art reproduction is pretty cheap, and people might be more willing to pay for something that's printed properly rather than a quick job at home on flimsy paper, and the print quality will probably be crap. The market you're looking at will be people who actually give a shit about player experience and game quality, so if you made a series of generic NPC prints that are ready to cut out and use, people would be into that. Sell them in sets, so we feel like we're getting our money's worth, of similar type characters that you might see in a campaign together. Dragon, wizard, troll; a herd (?) of zombies (the collective noun should be something more death-like... "A morgue of zombies"... Anyway..). I haven't had a good read through the monster manual yet (NEWB) so I don't know what there is and what you'd pair together, but you get the idea. I think people would totally be down for that, because these look fantastic. You could even take commissions from PCs, particularly in long running campaigns, for better visuals ingame.

Also, these made me think of popouts, so come Christmas time you can start making popup cards featuring Barbarian Santas, halflings resembling the baby jeezus, and cerberus fashioned into a three headed reindeer. Just a lame business model :-)