I use a mix of purpose-bought spray inks (glimmer mist, but I find the colour not intense enough), or the Adirondack color washes which are great, and some sprays which I have made up myself. For that I dilute regular india ink in water and add some perfect pearls if I want it to shimmer. I have also used the kids liquid water paints, diluted in water or some acrylic paint again diluted to a good consistency in water. This is the cheapest option and gives great coverage and colour, particularly for the primaries.
I have cut out lots of masks myself! The internet is a great resource for simple models and shapes (try: coloring+whatever). I cut them in bristol cardstock (very common school supply and dirt cheap! They don't last long, but they last long enough
to use several times. The big advantage of making your own masks is that you can adjust the size to fit your project.
I do have some plastic masks which I bought, and I use them mainly for background, as a change from stamps.
Thanks for the heads up on the paper range. I have the stars and hot air balloon papers from Lime Twist, but hadn't seen the bingo numbers or that cool stripey paper, nor the kites.
Have fun getting your hands inky!!!
Here's a page I made tonight. The red motif in the background (right hand side) is sprayed with Glimmer mist using a shop-bought mask. I then flipped it over and used the 'negative' side for the little detail on the top left of the photo.
In this page
the leafy fronds are a mask I made myself, and in this one
the various blue and golden rectangles are primitive masks which I also made myself. It doesn't take much to get a great result.