Ann,
I've done this - I print them on Epson Matte Paper Heavyweight (I don't like glossy), using the Adobe 1998 RGC profile, which does a pretty good job of matching my Apple display to the print. On the Illustrator file, I print thin gray lines that tell me where to score and cut to make the card. I set up the image in Adobe Illustrator, with the title of the image at the bottom center of the back, printed in light gray, with a copywrite notation. I can make small ones, 2 to a sheet of paper, or larger ones. Everything is printed on an Epson R200 printer ($100 consumer printer) using the highest quality settings. It makes a nice looking print at small sizes.
I buy white envelopes from a local paper and office supply, and thin, clear "bags" on line, to hold them all. The top is stapled with a fold-over printed (on the Epson) closure.
On the closure is my contact info, the statement that these are original "giclee" (that great marketing term that means "ink jet") prints
I have sold them in sets of 4 for $12 - $15 US, enough to break even, but not much profit. On the closure is a small thumbnail image of each of the card images, with one card visible from the front (4 separate images).
They sell ok, but the real idea is marketing the images. The closure indicates that silver gel prints are available, with contact info.
As mentioned above, it is labor intensive, enough so that I did one large run of 60 packets, sold at a gallery and framing shop, and an art center. As far as I know, I made no print sales due to the cards, although they were well complimented.
I have investigated commercial digital printing (I am in the printing business), but no available and practical solution has good enough quality, at least for me.
PM me if you want to discuss further (we're kind of getting digital here).
If you post them on your site, be sure to follow up with a link. I'd like to see them.