Though there are plenty of hotels in Dumaguete, to find a clean room under 600 peso should be possible but both with airco & tv!! Check Vintage Inn opposite the public market. Rooms are not luxury but they do have a small tv and airco and (but not all) a hot shower.
We attempted to check in to Go Hotel last night. Standard room was P998, about 20%+ more than numerous new hotels downtown. The place looked deserted so I am certain they were not "overbooked". Evidently in order to get good prices you have to book months in advance. Larry