What's the rough budget size for one person year (research asssistant/postdoc) in academia?
The total amount of funding is difficult to guess. If you can't get detailed information, it's better to just state the number of positions in the grant and the total duration. Even that could be left out. If you're applying within Germany, everybody will know what a "typical" DFG grant includes. For applications somewhere else, I'm not sure how relevant this information would be.

The personnel related funding received from the DFG is standardized. See for example there for rates in 2012. The important question here would be wether it's a full-time or part-time position. That is field-dependent.

Overhead cost is standardized at 20 % of the total funding (at least for recent grants, it has been less earlier).

Travel costs and other is really dependent on the project.