Whilst it is appreciated that you are seeking guidance based on other PC's experiences this may not be the way to go about it as no two toilets are alike.
A more comprehensive and in keeping with your obligations to give value for money as required you need to analyse exactly what the PC is prepared to pay for. This can range from 100% to 0%. You need to assess the value of this amenity to the community before you give any support. You then need to work with those that pay the bills (the village Hall) to assess the cost of running the toilets. Maintenance ,equipment replacement, cleaning, sanitary supplies (soap, towels toilet paper etc),portion of rates, water rates (or meter) insurance electric, heating etc etc.
Once you have ascertained the full costs involved, then you can agree what proportion will be donated by the council and how an annual review will take place to cover cost increases.
If you do this then you can completely justify the donation rather than it being based on an estimate of others. In other words you will do your job correctly as a council for the benefit of the community you serve.
Happy New Year to all