Hey,
let me start by saying im all for fee system implemented - the prices might be a tad too high, but if it helps the game economy so be it. I've encountered an 'issue' when trading with a preffered status player today. I got him an armor from GTN and then he would trade me a platinum dye for said armor. Well. The fee for him was 50M, and with preffered's credit cap of 1M (which is literally nothing right now, but its not the topic of the discussion) - it made the trade impossible. The thought behind the fees were to unscrew the economy, but it screwed the preffered players at the same time: because it took away their ability to trade item of any worth. What I'd suggest is adding an option to pay for the (trade/mail) fee from a legacy bay (same as an option to pay for item repair with guild's fund). I spent 2013-2018 as a preffered and I feel for them, also this would make QoL better for subs (ie: Im sending OEMs and RPMs to my crafter friend, and need to pay couple millions, I dont have that money on me, I have to run to the legacy bay to get them, ugh).
May the force be with you!
TLDR: Option to pay for trade/mail fee directly from legacy bay.