How much can I expect to spend on a 8 3/4" rear end?

The 8 1/4" rear end in my '73 Dart is an open unit with highway gears. Rather than screwing around with it, I would just like to upgrade to a 8 3/4" rear end. Any advice on what the going rate is for a decent rear end for an A body? Just looking at how much I need to budget for the upgrade.

Thanks!