How much porcelain/ceramic crown for tooth 7 and 8 usually cost? Which one is better metal/ceramic or porcelain/ceramic crown?

Varies by region. There is nothing more esthetic than a porcelain/ceramic crown and the research is showing that they are every bit as durable as porcelain to metal crowns. Fees range from 550 to 1100 per tooth depending on the dentist.
800-1400. If is hard to set a price on a procedure since high price does not mean a good crown and low price does not reflect a bad one either. A dedicated dentist would give you a good crown, regardless how much he charged (even if he was doing it for charity, it would be the same). All porcelain (emax) is the best crown. If the tooth is severely discoloration, use zirconia (another porcelain) core.