Although it's great for finer detail work because it's pre-thinned to a really good consistency, you don't really have to use artist's fluid.
Regular bulk liquid latex works just fine too, and you can get a pretty darn close simulation of maskol and other branded fluids via thinning it yourself with water and coloring it with acrylic paints. I bought a 4oz bottle of the 'Liquid latex Fashions' stuff on Amazon that I'm only now starting to run out of, thinning and coloring it myself which makes you end up with about 6oz in total. I see some even more large sized containers are available from other brands now too for even cheaper, 16oz for 8 bucks. I imagine they're probally pre-thinned, so might even work out better for masking use. Definitely a great option if you're budget minded or like to be very liberal with your application like I do.
I'd probably recommend still getting at least 1 jar of some of the artist fluid though, as it is a really great mix for super fine detail work.
