http://www.handloads.com/

In the right column is a calculator. This makes it easy to figure costing. Whether you buy primers by the hundred or the thousand, powder by the pound or 8 lb keg, it will break it down into cost per round. As long as you know the charge weight, just pump in the numbers and it spits out the answer.

And the Load data database in the left column is very helpful as well.

The usual disclaimers apply.