Could just make a separate mule and make it your go-between. It also has the added benefit of eventually becoming your personal WHM/COR/GEO/BRD mule if you so desire. Would solve your particular problem and one day prove to be a worthwhile investment for those times you and friends wanna kill $@#t but can't find a buffer
This option costs twice as much as having a single character and most people wanting a mule will just use it for synth/inventory purpose without the will to spend weeks doing all the missions to get access to endgame areas.
It is just HELP I AM TRAPPED IN 2006 PLEASE SEND A TIME MACHINE that in 2017 you can't still send over 1M gil between your own mules and are limited to 8 slots (I can sorta understand the latter for server load, 0 excuses for the former)
The cost of the pol account is valid but let's be perfectly clear, it realistically takes only a week to get a Mule in a usable condition. This includes limit breaks, Missions, RoV (it has short-set options for those who haven't touched other storylines)
You are absolutely correct; if all he/she wants is to move gil, finding a trusted party or AH are the best bets. However making a usable mule isn't very hard. I was just offering an option that could provide useful benefits if it sounded appealing