a poly running T-shirt at old navy costs 6 bucks, you can find similar at wal-mart. Fleeces are
easy and cheap to find at wal-mart, old navy, and thrift stores. This works fine for a base layer.

Wool is also very good and it's hard to beat a cashmere or merino sweater for this, check your local thrift store - I've picked them up there for 5 dollars.

synthitic shorts and pants are easily found in wal-mart, k-mart, zellers, etc. with the athletic wear, usually real cheap. Also findable at a thrift store.

You can do a pretty good job reading labels at a thrift store, and checking a couple discount stores.

Even for harder to find stuff like poly long johns, check work clothing stores, or use pantyhose with the feet cut out of them.

The only think I truly would insist on spending big money for at an outdoor store myself would be
my socks and my boots/trailrunners.