Disclaimer: I have no financial benefit from this article, it just reflects my personal opinion!
When it comes to printing QSL Cards we are facing many specialized QSL printers competing for a very small market with a huge price range. German QSL Shop for example is around 90€ for 1000 cards and 200€ for 5000 cards (glossy front and b&w backside). This includes some professional help in setting up the card and using standard backsides. This is a great service if you are not willing to design everything on your own!
If you are able to create your own design, or you have someone who can help you with that, you can end up below 50€ for 5000 Cards with a high gloss print on the front AND the backside! I have printed about 60.000 Cards with wir-machen-druck.de and I am very pleased with the speed and the quality of the cards! Cards were for: DF7ZS, LX7I, D4C, D41CV, CQ3W, P40Z, CT9/DF7ZS and more …
As they do not know anything about QSL cards you need to go to their website and look for flyer with individual size (Flyer freie Größe).
The best size for QSL cards is 14 x 9 cm on 250g – 300g paper.
I usually use the cards with a uv paint coated high gloss surface, but this is a matter of preference. Not everybody likes the high gloss cards and you can use them only for labels. If you want to write on the cards only a permanent marker would do the trick!
NO printing with laser printers or inkjet, no normal ball-pan only permanent markers would work!
Besides my „tick“ with the very high gloss paper you can select between different qualities:
The price for my selection is 35.30€ exclusive VAT for 5000 cards.
(prices are subject to change)
300g paper non glossy for better printing capabilities is about the same price.
After you selected quality and quantity you just need to upload your files and pay! Usually cards will be ready within one week.
Again … there might be other online printing shops out there, I am just suggesting the one where I personally had a very good customer experience!
For fairness reasons here are a few printer I know specialized for QSL printing:
http://www.qslshop.com/ (I have used them in the past – good service)
https://sax-druck.com/ (You can order cards including QSO data imprinted)
http://www.qsl.cz/en-qsl/ (I have used them for many years)
… and there is more out there: http://lmgtfy.com/?q=qsl+card+printing