If you want to get some ballpark figures on cost, try BP Medical. They're a medical supply house in New York that I use. Very reasonable prices, pretty complete selection.

I know that you can get AED's for less than $3000 retail. Mine cost me $1500 but it was bought as part of a group buy of 6 from the same vendor.

You might also try "AED Superstore", good, very good in fact on prices but I have no personal experience with them. Gotta love the name...;^)