There is a lack of those items being sold so people put them up for high prices because they have no competition. Before 1.18 brought loads of people back to the game there just wasn't much of a demand, now there is a demand. All it takes some enterprising crafter (either someone who leveled it a long time ago, or a new player taking up a craft) to realize this and exploit that demand for a big profit while leveling by undercutting those fools until prices are more reasonable.
In the meantime there is no reason you should be buying something at that level that is more than 20-30k gil, in fact some of the stuff you can buy from NPC's for less (look them up on a database such as ffxiv.yg.com), instead try and get some gear from guildleves/sidequests (
list of sidequests here) from that new Garlean invasion thing or find a crafter friend you can commission to make the items for you. That is what we all did when we first started the game.