If you are ok with gold and silver and don't care about the little rubber liner, you can get them really cheap at any wine making store. A bag of about 200 is around $12.00.
They can be flattened using a rubber mallet, or if you have one, use your Sizzix. I flatten 3 at a time using my red Sizzix with the sizzlets adapter attached. It's fast and easy, and always flattens nicely.
I'm making several stocking stuffers with these this year so lot's to prepare.
Here's the first batch. I made little rosettes with them. These will be strung to use as ornaments. I plan on attaching them to cards I will send out.
I used silver bottle caps on these. The images are punched with a 1" circle punch from a Christmas tag. After gluing the images into the cap I covered them with Ranger's Glossy Accents and let them dry 24 hrs. Each rosette was made from a 12 x 1" strip of patterned paper. I scored the strips every 1/4" and folded them accordion style. The centers were glued onto a 1" circle punch out with my glue gun. I then attached a bottle cap to each centre, again with my glue gun.
Here is one more made from an old Christmas card (I have 4 more like this one)