You don't need glossy or anything fancy, in this case thin and matte is better as you may want to write on the inside and it's easier to fold. Also looks more like a tag, not so much like a business card folded in half.
This is assuming you have a business card layout already. If not, I've used Studio Chic Design and Accentuate and was thrilled with the price and the result. Not sure if these sellers have Artfire Stores, worth a check though.
Take what would be the image on the front of your card and turn it sideways placing it all the way to the right end of the template. Place the image/info you would use on the back, turn it sideways and place it all the way to the end of the left side of the business card template.
You will be placing all the information on the front template, leave the back template blank. If you have stock that is always the same and are wanting to price the item, you can add that information to the BACK template.
To add the price/whatever take your text, again, turn it sideways. Place it all the way to the LEFT of the back template so that when you open the card, the pricing info is facing you.
Double check this, please. It's worth printing a preview so you can make sure the inside is correct. I've not printed them out this way, print a preview.
Do some fiddling to make it fit. I added text to make it more like a gift tag. You can see here I shrunk the front image a bit and added it to the back of the gift tage.
Double check to make sure you have the text and images facing the right way, I normally print a preview and fold it.
When your cards arrive, simply fold them in half and punch a hole in the corner. You'll have a nice blank space inside (this would have been the back of the business card) to write a note or price or whatever.