Really, the only time they need switching off is when you are changing, or otherwise disconnecting the batteries that the solar controller is connected to. Most solar controllers like to be connected up in the sequence batteries first, then panels. Some could be damaged by having solar in with no battery connected, but many can survive that. One way round this, with no switch, but with a bit of planning, is to disconnect an MC4 connector at the end of the panels the evening before. No sunlight means no big sparks and consequent errosion of the MC4 contacts.
The reason DC switches for high voltages and currents are so big and expensive is the arcing that you get when they are opened. With AC switches, the voltage and current are passing through zero a hundred tiimes a second, so any arc is soon extinguished, so the contacts can be smaller and don't need to be opened so far apart. For DC, the contacts need to be snapped apart as quickly as possible a sufficient distance to break the arc and the switches are larger, more expensive and complex to make for a given voltage and current. This gets harder, then higher the voltage. If you look at a typical switch for AC and DC, its DC ratings are much more conservative than its AC ones. A switch might be rated for 250V 16A AC, but only perhaps 12V 5A DC.
I have switch between my panels and the controller, but I only have 240W worth of panels, so a standard DC toggle switch is sufficient. For bigger systems, you'd need a bigger and more expensive switch, if you want this capability, like the one @blackrose purchased.
Jen