So this is a belt which was past down from my grandad and I was just wondering if someone could help me with where it came from and how much it is possibly worth. Any help regarding this is much appreciated
That is a belt buckle as used by the Wehrmacht from 1936-1945.
The slogan "Gott mit uns" is taken from the bible: Judith 13,11 and Matthew 1,23. It has been used as a battle cry since at least the Thirty Years' War and was declared the official motto of Prussia in 1701. From 1847 on, you can find it on the belt buckles of Prussian military uniforms – looking largely similar, except that the center featured a crown and the lower half of the circle featured a laurel wreath instead of the oak leaves.
The Reichswehr (the German army during the Weimar Republic) uses belt buckles adapted from the Prussian ones, with the crown substituted for a Reichsadler (sans swastika, of course). Incidentally, the Reichsadler of the Weimar Republic faced left and the first design still uses this left-facing eagle, now sitting atop a swastika and the laurel wreath replaced, as I've said, with oak leaves. The change in the direction the eagle is facing is not without significance: while the left-facing eagle represents the German state, the right-facing eagle was considered the symbol of the NSDAP. So this change from left- to right-facing symbolically put linked Wehrmacht closer to the Nazi party than to the German state.
The German Bundeswehr continues to use this motto on their belt buckles until 1962, when it is replaced with Einigkeit und Recht und Freiheit. Police forces change the slogan during the 1970s.
Now, as for how much this is worth – I can't really judge that, but my guess is "not much". I'd wager you could maybe get some money out of its "emotional value". Mind you, I'm not referring to the emotional value this buckle has to you or your family. But there is a certain clientele which would give you at least some money for it. Though honestly, I wouldn't want to be trading with these fine historically-challenged folks. I suggest you ask the nearest museum (ideally a memorial), they might tell you if and where the buckle can still be put to use.
You might try posting this in r/whatisthisthing. It is often amazing at identifying obscure objects.
It's a German Army equipment belt of the kind in service through much of the war. In its present condition, I wouldn't expect it to be worth more than $200 or $300, if that much, but I could certainly be wrong.