The DEP like the Glock cannot fire lead, but for different reasons. Lead will foul up the gas system of the DEP. You don't see AR-15 shooters using lead slugs for the same reason.
Now I haven't looked in a while, but last time I checked, the dies were 200 bucks for 50ae. Then the question is do you reload and shoot enough to make it worth the expense.
Wasn't sure. It was near when the 50 ae first came out, so I guess they were out to gouge people for their tooling costs then incase it didn't hit big.