As I said @Kristina373 you need to itemise what support you are looking for so co-hosts can give you a quote for the services you need. Some hosts want full support some just management of communication with a guest, for example.
What exactly is it that you want them to do? That would be my starting point. If you want to look at various options ask them to quote for them.
Your co-host should be providing you with a draft contract @Kristina373 including a breakdown of support being offered and costs and payment terms. I paid a solicitor to draw mine up based on my requirements.
I know some hosts and co-hosts work on a percentage of bookings made, ranging from 10% - 50% depending on services needed. Additional for emergency out of hours support. Of course it will depend on your day rate. 10% of £1000 a day booking will work out at far more than 50% of a £40 a night place.