I think we should recommend to use the three letter ISO 4217 standard currency codes (https://en.wikipedia.org/wiki/ISO_4217) instead of the one unicode characters. So $ should be USD, € should be EUR, etc. Many currencies don't have character symbols at all.
Also we should expect to have a space between the amount and the currency code.
Amount should be used in US format, so using . (full stop) as the decimal mark to separate the integer and fractional parts.
Apostrophe ' would be optional to separate thousands.
So the examples would look like:
charge=May - October Mo - Sa 8:00 - 16:00 1.5 EUR/2h
charge=16 USD/hgv; 8 USD/motorhome; 6 USD/motorcar
charge=4 USD/person/day; 12 USD/person/week; 0 USD/child < 14years