Has anyone come up with a good fix for this problem? Just a regular, cheap, plastic mask. I hate how I can't wear it for longer than 5 minutes without there being moisture dripping from it >.<

Can you upload a photo of the mask?

There are several options - most are to make aspects of the mask mesh/or put holes in to allow ventelation. But depending on the mask type/cosplay it's for this may or may not be useful

You can buy sprays that you spray inside but I've never found them that useful personally

It's just an Anonymous mask
Just like this: https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSuVdF-gN5hioJmN9K4SyimNnOaPWycPCDE-buI9G_nFXT7dp0Oww

Cool I would be tempted to drill a hole or cut with a stanley knife holes into each nostril to remove it allow you breath out of the nostrils and see how this improves it.

If this doesn't help you may need to consider making holes in it for the mouth area.

I have also heard of people putting gauze on the back of their masks to help soak up any condensation produced but depending on how long you want to wear it and how thick the gauze is it could get saturated pretty quickly

Also the eyes in the one you've linked are cut open. If this isn't the case for yours consider cutting eye holes and filling with black mesh

Try this article:

http://www.scubaguru.com/index.php?option=com_content&view=article&id=57:how-to-defog-a-diving-mask&catid=41&Itemid=54

Spitting is pretty horrible but surprisingly effective XD Baby shampoo, on the other hand, is bad for your eyes (strips the lipids from the tear film) but as your mask is not airtight, it should be ok.

That is a mask of V from V for Vendetta. A character which Anonymous has borrowed with great effect. I had the same issue with my own.

Some sponges can space it from your face a little better, which means less plastic touching your actual skin.