NOW is a good company. I've tried different brands of ZMA and they have all had similar, good results. It should be cheap regardless of which company you choose and be sure it matches the original Conte/SNAC blend as some companies like to throw in extra stuff like tribulus I use Primaforce ZMA and I get a 2 month supply for about 18 dollars. I am sure NOW is just as good though.
Know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? For ye are bought with a price: therefore glorify God in your body, and in your spirit, which are God's. 1 Corinthians 6:19-20
I beseech you therefore,brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. Romans 12:1