The reason you don't hear much about this issue...
Even the Democrats think that it would sound a bit bizarre to complain about a benefit to the elderly costing too much.
The main gripe they have is that Bush's name is on this latest highly-inflatable wealth-redistribution boondoggle (and boy, am I just tickled pink about THAT) and not Ted Kennedy's. You have looked at the Kennedy proposal and its costs, haven't you?