Cheap Paints

in general enamels are cheaper, but since they are more dense they come in smaller tins. Compare tamiya acrylics even the small package with the humbrol enamel

Sean:
The problem with cheap paints is just that: they're cheap. You'll discover some brands of paint might also be overpriced but cheaply made (Testor's comes to mind). My advice: Try not to worry a lot about prices, but use the brand of paint which works best for you and your style of modeling, and a brand which offers the range of colors you use most.
As for which formula of paint is cheaper: It's pretty much a dead heat. Pricing depends a lot on how much paint you get in a tin or bottle, and the price of oil (like everything else on earth). I use fairly expensive paints (Humbrol) but I also know I get a lot of value for the prices I pay; some of my tins of Humbrol colors are 10 years old and still useable. The few Testor's colors I have bought have turned to gum in a few months. Hardly worth the expense. The Tamiya Acrylic colors I have used also last a long time. So it all comes down to getting what you pay for. If you pay a little more for your paints, but they last a lot longer after being opened, then that is a less expensive paint.

Sean,

Most of the time, you'll find that paints from a certain manufacturer, whether Acrylic or Enamel, run the same price range, give or take a few cents. As to which ones to use, check out more advice on this in the General Modelling Discussions or Techniques forums.

demono69