I found these on amazon, it says in the Q&A that with some effort you can clean them off after using dry erase.
I bought some blank white glossy cards on Amazon a while ago. Basically InfiniTokens but completely blank a lot cheaper, I got a 50-pack for $5. They work perfectly.
As a tabletop prop I would start with this :
https://www.amazon.com/Blank-Playing-Cards-Glossy-Advantage/dp/B001UG392E
For myself, I look at it this way: the multiverse is HUGE - out there somewhere in the multiverse is some god of luck who fosters a dedicated monastery where a cloistered bunch of fellows dutifully turn-out these devotional items (the are probably working-off gambling debts). This has been going on for a very long time and the decks have made their way through the multiverse to arrive here on my game world.
Maybe your PCs get caught-up in a situation where a friend with a gambling habit is snatched away to toil in the monastery?
I think they have blank cards that you can print directly on Amazon: https://www.amazon.com/Learning-Advantage-CTU7387-Blank-Playing/dp/B001UG392E/ref=sr_1_4?ie=UTF8&qid=1511467892&sr=8-4&keywords=blank+playing+cards
Pretty cheap and via Prime. Depending on the volume you want, that may be possible.
I recommend something like this
for readability compared to playing cards with sharpie written over them
I guess the simplest way would be to take a pack of bicycle cards (which are the same size) and a sharpie. But you can buy blank playing cards on amazon but if you wanted the Cards Against Humanity words printed on the back you could look into screen printing kits or get some sort of custom ink stamp made online.
For completely custom made cards, this place make custom decks both front and back for $12 for 1-5 decks
I've had good luck with extra glossy blank playing cards and a dry erase marker
If all you're looking for is good looking cards with a little text on them, I'd recommend picking up some card blanks. Shop around, I'm sure there are cheaper options, but the card blanks I've used in the past take a sharpie well and play just as well as a normal deck of cards. Use multiple colors of sharpies to help distinguish different types of cards. Take it from my experience: Don't bother with any clever graphic design until your game is solid.
If hand-writing your cards won't do it for you, and you're just looking to place text on cards, then I'd recommend looking into card-making tools like MTG Set Editor. This will let you create an image file of cards, which is the first step towards getting them professionally printed. MtG layout is the default, but it's easy to make a new template to match whatever you want.
If you want someone else to design the visual layout of your cards, keep in mind that this is a VERY involved process. You're practically asking someone to design half your game for you. If you want professional quality card design, you should hire a professional graphic designer.
Once you have images of your card game ready, then check out companies that specialize in printing playing cards. GameCrafter was recommended elsewhere, but I've found that Printer Studio is cheaper to use. If you only want to make a few decks however, go with whatever option seems easier. When submitting files to the printers, you'll need to provide what's called "Bleed files". These are images of your cards, but with nearly half an inch of extra border around the outsides. Printer Studio provides templates for your bleeds, and it looks like Game Crafter does too, so check those websites for the resources.
Source: For the past two years, I've been developing, creating, and selling a card game out of my living room. It's been pretty damn successful in its little niche, and the advice I've given above is what we've used to create our game.
Glossy blank playing cards and a dry erase marker
Cool, we use these, I like the feel, though they aren't reusable.
http://www.amazon.com/Learning-Advantage-CTU7387-Blank-Playing/dp/B001UG392E