Spam Random Normal dungeons, it is 3~5 minutes run and each will give you 25 gold (on level 50) bag.
Fast rush of high prime Infestation / M-13 will give something near 20-30 gold per run. Slower than last method, but need only 1 person, not 5.
Collecting behemoth meat and sellign on CX.
Carfting potions as Technologist.
Doing Contracts. Tier 5 reward gives 2.5 plat and if you take toy/reward bag, after some time it will be giving extra 7.5 plat, so it is 7.5 plat roughly every 4-6 days.
Doing BG's / PvP Contracts for 2.5+ plat, faster as need only 3 tiers to give maximum tier reward, however, need for PvP to pop.
Just doing Dungeons and Raids. If you have guild repairs or you are not wiping, full raid run will give near 6-10 plat (especially if you are Elder Gems capped and using experience potions, so all experience is converted to money).