You only need 30 coins per weapon. I'm usually done with the NM part of the trial in a few days or so. You can solo some empyreans but it takes FOREVER that way. I know some people who solo/soloed em. Also it takes way more effort put into and time. TO ME they are not worth it, especially if you are like me and hardly ever play the jobs you are farming one for. If you play the job a lot then by all means farm an empyrean. Kannagi/Almace is probably the easiest and less time consuming path to take. Chloris and Ulhushida are easy but damn Chloris is hell to farm. To each his own.