>>> I just discovered this today playing at the monster arena..
after beat Nemesis a couple of times, the battle with Fenrir become free.
of course you still need the 8000 + gil for start the battle but after that just keep fighting him and you dont lose any money after the battles. also the this monster start to drop expensive weapons and you can sell them for 60000 + gil..
Im not sure why this happened, i guess is because I beat nemesis a couple of times but maybe there are other variables involved..
1- it seems this only work with Fenrir, but I still have to test other monsters yet..
2- it seems the method and the characters you use for kill Fenrir doesnt affect the glitch..
3- Im playing the US version..

This sure work in my game but i still need confirmation for this, so if this work for somebody here too, please tell me..