Is there a cap on how much I can receive through the NDIS?

The only limit on the supports the NDIS fund for you is what's reasonable and necessary for your disability.

There is a price guide for support services, this is based on what the NDIS think is fair, and they'll pay that price for supports. If a service provider charges more than that price, and you don't self-manage and want to use them, you'll normally have to pay the difference.