The Hidden Tower is not closed. Occasionally it shuts down for an hour while Fyora is off doing other stuff but it isn't closed. I'll add that only three paint brushes are available there, so it hardly controls the cost of them all. If you go repeatedly and it doesn't work, your Neopets account is probably under 4 months. No user under 4 months can access it.

The reason PB prices are inflating is that people are buying them to use to paint pets to trade through the pound. It used to be against the rules but TNT now allows it, so, in order to get more "valuable" pets, or just to make their pet's paint job more valuable, people are buying and either using or holding onto the PBs, which inflates the prices.

It's all disgusting.