Found availability for 4 nights in early Aug at Vessel Hotels' Katsutadai location for 28,000yen/night + tax for 2 adults in their twin room, breakfast included. That is a legitimate hotel chain and located about an hour by train from Ueno. Only problem is the room is 19m2 and, while that is not bad for Jpn, I have not stayed in a room that small in many years. Anyways, this hotel wasn't available before, so I think it's worth checking all the time to see if anything comes up.