All of the exhibitions I take part in allow card sales as part of the display. Whether hand making mini versions or professionally printing this is another string to your bow, a small income stream and spreads the word about you as an artist.
I often use up cut offs, trial paintings, or bits of paintings I don’t like, as a basis for the mini paintings or pieces of art that end up as a lovely card.
Not only is this a way of get back exhibition fees, it a way of spreading the word and website out there.
Card blanks and cellophane covers are out there on the high street, easily found in places like the range, hobby craft and online.
Stepping up to the next level having Cards professionally printed there’s plenty of alternatives.

Original artwork, scanned and printed on home printer on handmade Indian paper.
Drying on the Aga!

Online you can upload photographed or scanned artwork and add text, order smallish quantities, sometimes getting penalised for small orders, enticing you to buy more than you really need. It also takes a few days or weeks to get deliveries.

Local printers offer card making services, there may be a set up charge but if you regularly order this can be kept to a minimum. Either a scanned or photographed image on the front and text inside and in the back. I can buy a few as 25, and reorder as I need.

I often have five or six designs printed and sell them in packs of 6 for the price of five. Tied with a ribbon and a label, they sell like hot cakes.