Magnus

Don't stop collecting coins, and when you complete your cape, show it off to us =P

Empress cape for anything but mages = no money. An equivalent of 5 Tempest rings would set you back (marginal cost) 125 million for a Helsium cape (though to be fair you can pchaos the hell out of the empress cape). Nope don't have the money, nope nevermind.

Hadriel

If that was to me, I don't farm coins for a nova cape =s. I'm actually seeking a shoe and maybe belt (too bad no belts in shop). I will admit that I actually did manage to obtain 2 nova mage capes off normal Magnus though =s. Sadly, I don't use mage equips anymore lol.

edit: @SaptaZapta (forgot to reply on that)

Did you turn it in to Maroon or one of the merchants?
Maroon only gives 1 coin, Gallero and Romero give 2. In my experience.
(No, you can't choose who to turn it into. The quest tells you.)

I was sent to Popo the pet looking npc near the old guy at eurek's hut.