Unfortunately, I'm not sure whether you saw my last discussion posts at another question, since you've never commented on them.
Brief explanation:
1) The phrase is not ambiguous.
2) I don't believe the answer is based in Swiss or Austrian German.
3) The important part is the preposition ("mit").
Example of a German sentence:
"Für eine Weinschorle wird das Glas je zur Hälfte
mit Wasser und Wein gefüllt."
Pour equal amounts of water and wine into the glass.
"Die Weinschorle besteht je zur Hälfte
aus Wein und Wasser."
Contains equal amounts of water and wine.
The Swiss Franc amount stated is only
one-half of the total amount. In contrast to the example above, you don't repeat the number, since it's twice about the same thing (money; not even German is that repetitive in terms of sentence structure).
Although Michael's answer seems to be the most helpful of the lot, I'm hesitating to agree, since this is not the wording a court would use, IMO.
"shall be obligated to pay one-half of such fee"
https://www.cga.ct.gov/2016/act/pa/pdf/2016PA-00026-R00SB-00...