Entryid of the creature.
The amount in 1 stack.
How much you can buy of the stacks.
The time (in milliseconds) before you can buy stacks again if you used your max_amount.
Extended_cost (items you have to buy with tokens etc.)
Here is a link with alot of (meanwhile outdated) extended_cost: http://www.mmopro.net/forums/discussion/558-every-extended-cost-id.html
Fresh values can be found in ItemExtendedCost.dbc.
CREATE TABLE `vendors` ( `entry` int(10) unsigned NOT NULL DEFAULT '0', `item` int(10) unsigned NOT NULL DEFAULT '0', `amount` int(11) NOT NULL DEFAULT '0', `max_amount` int(11) NOT NULL DEFAULT '0', `inctime` bigint(20) NOT NULL DEFAULT '0', `extended_cost` int(11) NOT NULL DEFAULT '0', PRIMARY KEY (`entry`,`item`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 COMMENT='NPC System';