The Deutsche Bahn
website gives you the journey prices, so you just have to do the maths. Except that you don't, because for some inexplicable reason I've done it for you.
FRA-NUR costs €45
NUR-HAN costs €86
HAN-FRA costs €75
They don't have prices for international trains on the website, but any Bahncard discount will only be valid on the Germany stretch, so you want to make sure you travel via Munich and not via Switzerland. Frankfurt to Kufstein (on the German/Austrian border) costs €91.
Total cost for all four journeys (within Germany): €297.
Cost of Bahncard 25: €53
Savings with Bahncard 25: €74.25
Cost of Bahncard 50: €212
Savings with Bahncard 50: €149
So you'll save a grand total of €21.25 with a Bahncard 25, half of which you now owe me.