i bought clams at a seafood shops and they are alive and well in my tank for over a year!
my buddy who told me about it has had the same ones for a couple of years.
btw, they were packed in ice!!!
and if you do search on cleaner clamson this site, I have directions on how to wake them up from their frozen sleep.
although they hide underneath the sand, they are really cool bc shoot out water and you see just spirts coming out of your sand.
although if you want that many- it might not be a bad idea the deal you are getting simply bc the mortality rate will be a lot higher on the store bought ones verses the ones that you will be buying