What are the most valuable items? Dragon Egg and Nether Star are up there, what else? Nothing more common than Diamonds, please.
If I had to order them (by what you can obtain on EMC) and what I personally would think reasonable for them. Dragon Eggs (last auction was for 2 million rupees). Beacons (30k average but dropping) Nether Star - Beacon minus 100r Wither Skulls (5-10k) Diamond Block -405 rupees Emerald Block - 315 rupees Emerald Ore - 250 rupees Anvil - 155 rupees Diamond Ore - 100 rupees Gold Block - 90 rupees Iron Block - 50 rupees TNT - 50 rupees Diamond - 45 rupees There's also enchanted items which vary wildly between a few hundred rupees and thousands. Books can also have a wide variation depending on their content. The vault currently doesn't handle them though. I'm not sure what the shop is selling them for, but chain armor as well could fall into that list.