購入【こうにゅう】
purchase, buy
購買【こうばい】
procurement, purchase, buying, school store, co-op, school canteen, tuck shop
購買力【こうばいりょく】
buying power, purchasing power
購読【こうどく】
buying and reading (book, magazine, etc.), subscribing (incl. free subscriptions), taking (e.g. newspaper)