Don't get me started on Airport Hotels and breakfast charges! Even at rip-off Heathrow you can still get far better deals in the terminals than in the hotels.
Heathrow does actually have a very good internal bus network. In theory you are supposed to be able to get on any bus for free as long as you are travelling within the airport complex. However some operators like the Hotel Hoppa will still try and charge you for a service you can get for free.
The trick is to leave the hotel, and walk behind it onto the Bath Road. From there you will see a constant stream of red London Buses, of which after waiting for no more than 5 minutes you can be guarenteed to find one heading to T4.