I charge £3 for 8x8 and A5 cards that people ask me to make, mostly with names on them (which is dead easy with the Cameo), but most give me £5 and tell me to keep the change as every penny goes to Sightsavers.
For Christmas cards, I batch make about 15 of each design and they're smaller - 6x6 or 7x5. I sell them for £1 each or 6 for £5 and they always sell out. I used to put them all in cello bags, but I don't bother any longer as my colleagues just choose what they want from the boxes in staff rooms! But I don't use ready made toppers as sentiments are always in English and my cards are in Welsh! So I suppose I have a ready made market as there are very few nice Welsh cards in shops!! I send Sightsavers the money about three times a year and it's always around £100-£150, sometimes more after Christmas.
I think that selling 3 for £6 or whatever would be a good idea. My mother and a few of her friends ask me to make cards without sentiments so that they've always got a store at home. Some for children, boys, girls, men, women, get well etc.
Good luck!