Check bead stores in your area. A lot of them carry Swarovski crystals and you can usually get them either loose or in small quantities to try out, or you can get them in bulk if needed. 
I have used them. I love using them. but I also make sure that I am the one serving the cake. To make sure all are off it before being consumed!!
I get my crystals from http://www.firemountaingems.com/
I love that place. They are so great and shipping is only $5 no matter how much you buy. Also the more you buy the CHEAPER they get. I have literally saved hundreds of dollars compared to buying at michaels or hobby lobby.
Beware though!! Crystals are addictive!!
I've done one cake with s. crystals (green & pink tiered cake in my photos). It is very beautiful to use them as centers for fondant flowers. I used gum glue (tylose & water) to hold the crystal in place in the center of the flower. I bought small, crystal rounds @ a local bead shop. I wanted flat backs, but they didn't carry those. I don't think that the craft shops have real s. crystal. Charge the customer the cost of the crystals.
How do you figure out pricing? The same way as any other item? How do you attach them on BC or on fondant?
take total price of purchase ( s&h) and divide by how many crystals in pkg and that is cost per crystal.
I use RI to attach crystals.
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