As always I'm a fan of the thrift store. All my winter and rain pants are from there. Look for a lightly used pair of waterproof nylon pants with an elastic waist and elastic around the ankles. I've found the kind that don't have any lining inside except for a light mesh. These effectively keep the rain out, block the wind, and keep the warm in (sometimes a bad thing if it isn't too cold out). Although I don't really think any rain pant really breathes that well.