were can i buy dry ice and how much does it cost a pound?

Answer 1

Places called meat lockers or refrigerated warehouses will often sell it to the public as they make it to chill frozen products in shipment.
go here http://www.dryicedirectory.com/
or google 'dry ice cityname'

Answer 2

any grocery store.

the prices vary widely, but you will have to be a certain age depending on the store to buy it.