For tires, you might just hit up the local hardware store. We have no LBS and the rear sidewall blew out on my freeride bike just before the weekend, so I got a $25 Kenda 2.35x26 foldable(kevlar bead?) rear tire, and it doesn't seem to give up anything to my fancy $60 Maxxis minion DH front tire.
Also the best comfy budget seat I've found is the Plant Bike ARS model. I bought some pedals from Chain reaction and it was a painless process and they had the lowest price I could find by far, for shipped to Canada atleast.