Polyp prices vary with some color morphs fetching over 100 bucks per polyp. Its supply and demand that determines prices.
A low supply of a sought after item will fetch a high price. The price of 10-20 per polyp is actually pretty common for uncommon zoas. Only way you will find them cheaper usually is at frag swaps or from someone who has a good size colony.
Many times Online stores have such limited quantity that they initially price a certain coral for many times its value. How much someone is willing to pay for it will determine demand and they then price accordingly to prevent going out of stock
29g Mixed Reef, 150w 14k Phoenix MH w/ Moonlights, Reef Octopus BH1000 HOB Skimmer, Ecotech Vortech MP10es, ReefKeeper Lite (Plus), PH Probe, Temp Probe, ATO, Carbon/GFO Reactor.