Whichever colorant you decide to use, they all cost roughly the same amount so you won't be saving any money unless you have unused makeup lying around.
Makeup
Before you buy pigments, I'll let you in on a secret. Most of the pigments used in makeup are the same pigments used in paint. Have you ever tried to get makeup out of your clothes? The photo above is the First Edition 120 Color eyeshadow Palette for $12.50 by BH Cosmetics. They have an 88 color matte palette as well for $11.00.
The color load will not be the same as with pure pigment. It will have a transparent effect, but that may be an advantage. Makeup also contains fillers that are not present in paint. BH Cosmetics, Elf, Sally Beauty Supply, and LA Colors (Dollar General Store) have the best buys.
Grind powder makeup and use the same as pigment. Add talc to thicken liquid formulas. Use cream formulas, wax eye liner or lip liner and lipstick for making oil sticks or oil pastel. Do not use lip gloss or mascara; they are not good for painting.
The one problem you're going to run into with makeup is the limited amount of reds in eyeshadow. Red is generally reserved for lipstick because the dyes and carmine used are generally not safe for use around the eyes, though there are some exceptions. You will have to use the same lake dye used for lipstick or paint for the red spectrum. The only red palette I found is made in the UK by Sleek. It's the Good Girl palette, but it was discontinued so good luck finding it. There is also a 252 color palette on eBay for $13.35 that has a few reds in it. MAC has a few reds in their collection as well.
Use face powder or loose mineral foundation for skin tones. The two palettes above are from Light in the Box for $13.99 each.
This powder foundation, blush, and bronzer palette is part of a kit from Light in the Box for $11.99.
This nude blush palette is from BH Cosmetics for $10.00.
This highlight and contour palette is from BH Cosmetics for $14.00. Use it to make highlight and shadow paint.
Alex Artist Colors on Etsy sells artist pigment for as low as $2.75/30 grams. That's the best price I've found and they have an excellent selection of ochres and oxides direct from Cyprus. They have some pigments that TKB doesn't have.
Kremer Pigments has the largest selection of historic crushed stone and earth pigments at $4.75/100 grams.
Ancient Earth Pigments has this great artist introductory kit for $35.00 and you get to pick any 12 pigments for the kit. They also offer 5 grams of any pigment for $0.75. They don't have a large variety, but they do have some new pigments that other sites may not have. They also sell carbon black.
TKB sells a collection of pigment samples for $11.65 and lake dye samples for $14.65. Any pigment sample is $1.65/6g. This is also a good place to purchase makeup blends and titanium dioxide. They have the best price, but not a large enough selection of matte pigments for artists. Pigments can be prewetted with alcohol, but lake dyes must be prewetted with glycerin or dimethicone. They're also prone to staining. Food coloring can be used with water based formulas because it is made with the same lake dyes. However, it will be very diluted and not as vibrant as the powder dye. Wilton gel coloring may be a good option depending on your formula.
Mica
Use bismuth oxychloride pearl to add an iridescent shimmer to matte pigments or custom blends. TKB sells it for $6.45/oz.
Dye
RIT Powder Dye $2.98 at Walmart. Fiber reactive dye can be used to make fabric paint or markers, but it's use on fabric requires that it be mixed with a mordant. The fabric must also be soaked in washing soda and dried before coloring. Rit now has all their dye color formulas on an iPhone app. They are no longer available on their website.
Glycerin based non-staining salt dye concentrates for coloring soap are wonderful for making transparent paint. You can purchase a dye collection from TKB for $27.65. Ninety seven concentrates are available for 1.65 each.
