DOH! I knew there is something missing that I don't get , otherwise it sounded quite weird.

Well if you arrive at HND around 10pm, you might miss the public transport if you get delayed or out late. Or you could catch the last few trains to Roppongi and spend the night drinking in a bar (they open til early as some office workers do that when they missed the last train home on Friday).

I noticed Chiba Stadium is in between HND and NRT. There are a couple of large hotels there. Assuming there is no event/expo at the stadium, you might be lucky to get cheap room rates. But do note Chiba Stadium area is quite out of town and has nothing much to see or do. If all you want is cheap lodging its something you can look into