I never use specific biking shoes. I wear orthopedic shoes (typically from Drew or PW Minor, but I buy them at deep discount on eBay). They come with two pairs of insoles in them. When worn with warm socks, and with the rest of my body well insulated, those are enough to keep me warm on even the coldest days. (For example, I biked 10+ miles in 9 degree weather yesterday, and my feet never got cold.)
