is there a way to view directly via the router without having to 'download' it from the web ?
If both your Slingbox and iPad/computer are both on the same local network accessing the internet through the same router; then they aren't running through the web and are communicating over the network. If your iPad is on a 3g/4g network...then you need to connect to your wifi network.
I don't know where you're seeing the "download is 10gb" bit. on the iPad, provider data usage? Your local network traffc will be very high..but that doesn't matter.