I have a Navigo card - how much to RER B to A from CDG to Disney
With a Navigo card the week subscription cost is 30€ and that will cover CDG to Disney on RER B and RER A. It's not possible to store single-use RER tickets on the Navigo / Navigo Découverte card.
If you're meaning the Navigo Easy card, you can put a 1-5 zone Navigo Day pass on it that will cover CDG to Disney. The cost is 20.10€ as of 2023. Otherwise, it's not possible to use Navigo Easy for the RER B nor RER A trains. It can only store single-use tickets for Paris Metro/Bus/Tram tickets, Roissybus, Orlybus, not RER.