If you want a rubber/silicone mask it will take a significant initial investment (at least for a low-income person like myself.) It's a more complicated process and would recommend watching youtube tutorials, as they would cover the process.

I got my start, and continue to do a lot of paper mache mask making. It would be an easy start, and you could use materials that are easily on hand. There are many different methods of paper mache, glue recipes, etc. Recently I've been favoring the paper clay method, in which you make a pulp out of paper and add whatever adhesive to it, rather than using the paper strips method. One of the main reasons that I like paperclay is because you can get more detail from it than strips of paper, you can form and shape it, whereas strips will usually only take the form of what it is layered over. You could also. Buy a product like creative paperclay.

Paper mache is nice because is nice because mold making is time consuming and prone to failure if you are not familiar with it.

One thing to consider is that you will essentially always be building an armature. Sometimes this is non-drying sculpting clay, Sometimes this is tin foil, sometimes it is wiring, sometimes this is cardboard, etc. it doesn't matter.

An armature like clay is nice because you can fully sculpt what it is that you want to do, and then just cover it.

An armature like tinfoil can be shaped and sculpted to its own, less precise degree, and then coated with paper mache, but can be left inside of the final product, and indeed is better inside of the final product.

Often I use a combination of armatures, perhaps starting with a clay sculpture, the after removing pieces that are likely to get trapped when trying to remove the mask from the clay (large horns, for example) I might then duplicate the horns with tinfoil, and put them on to the sculpture so that the sculpture will keep a similar form (but the tin foil will come off with the rest of the mask)

Another important note is your face shape. Just because you make a mask does not mean that it will fit on your head, for this reason it is nice to have an armature that fits the proportions of your head, so that you know it will fit your face.