I love finding inexpensive makeup and skin care products, but I hesitate to spend any money on a product I'm unsure of. I've come to value Paula Begoun's cosmetics evaluations for her honesty and straightforwardness--and for her attention to great, low-cost products. She reviews cosmetics in all price ranges and lists approximate prices in her reviews. She just came out with her Best of 2007, which has a few rather inexpensive items--I paid particular attention to the e.l.f., Jane, and Rimmel reviews (remember the $2 Jane coupon here).
Paula also offers a searchable archive of product reviews that I check when I'm looking for a new, low-cost makeup item.