How can I figure the real long-term economic costs of bond issues and state/national debt?

This gets complicated. If you assembled a room full of economists, they would probably give you many different opinions. The problem is that there’s no truly reliable model for macroeconomic projections, and opinions are always colored by political leanings.

In spite of this, you still can make some sort of estimate. The first thing to do is to choose which model you want to use, and then to plug in numbers. The result may be inaccurate since models don’t always reflect reality.