When I paint figures, I may (or may not) wash and rinse them in warm soapy water to remove any mold release agents. After they dry, I'll spray-bomb them with a cheap gray rattle can primer. After that dries, I go to work on them with el-cheapo craft store acrylic paints. I keep a fair selection of basic colors on hand, but you don't necessarily need to keep a lot of shades in stock. They're so inexpensive, that if a color is a little too dark, or a little too light, or not quite the right shade or hue or color, you can mix as required to get what you desire! I keep a bunch of small plastic cups around (i.e., little plastic ketchup cups from a fast food joint) that I squirt a little paint in (only about what's needed), darken or lighten or tint as desired, and do my brushing. I use a couple of other slightly bigger cups to put water in for brush cleaning.
When I'm done, it's all water cleanup (brushes AND cups) with virtually no wasted paint. 
