If you want 32 slots, get that thru discovery too.Look up the discovery recipe for the 28-slot version on the Wiki and craft it.Craft the 24-slot version and make sure not to equip it yet (because 24-slot and 28-slot bags are Soulbound on equip!).Buy the relevant 24-slot recipe from the TP (or gamble for it yourself in Desert Highlands, but the TP is about the same cost and easier).Get to Crafting level 500 in the relevant discipline for that type of bag, on any toon.Otherwise go with either Armorsmith or Tailor, because Leatherworking materials are more expensive. Some of them have different sub-types for different crafting disciplines, in which case choose whichever one you've already gotten to level 500 on some toon, or plan to. Craft or buy the 20-slot version you want (that is, whichever one has the properties you want-generic, materials/upgrades, equipment, junk, invisibility, or containers).I saw that forum post about the 3x 18-slot bags too, but I'm not aware of any such option. buying them from the TP, but the cost doesn't vary much regardless. There are a few variations along the way, such as obtaining materials yourself vs. Otherwise there's only one method to get any >20-slot bag, which is to craft it yourself from a 20-slot bag. As far as I know, the only >20-slot bag you can get from an achievement is the Reinforced Olmakhan Bandolier (32-slot bag from LW 4.2, Sandswept Isles).

Gw2 cheapest 20 slot bag