My vote also goes for the Royal Park Hotel at Terminal 3. As OP mentioned there are a lot more reasonable options in the vicinity of HND. But OP only has 8 hrs. and I do not think it is that much worth spending time getting to/from the airport. Stay at Terminal 3 where OP will be departing from. The Royal Park Hotel at Terminal 3, rooms are a little bit on the small side. Rooms are more like Japanese business hotels rather than Western chain hotels. The hotel has a restaurant but Terminal 3 also has restaurants on the non-secure side of the terminal, two of them open 24 hrs. There is also a convenience store Lawson located at 1st. fl. of Terminal 3 (arrival level) open 24 hrs.