購読[koudoku] paid subscription (e.g. magazine)
購読料[koudokuryou] subscription charge
購入[kounyuu] purchase
購入者[kounyuusha] purchaser
購入注文[kounyuuchuumon] purchase order

購買[koubai] procurement
購買力[koubairyoku] buying power
直接購入[chokusetsukounyuu] direct purchase
購う[aganau] to compensate
購入先[kounyuusaki] retailer