hyoriiiiiiiin and he's oly 2800 gold in one of those on going events if u r on US server i.e :D ultimate hero i guess
I got Hyorin on my 2nd Account during Ultra Hero. Only needs you to top up 2800Gold (70$ iirc).
Imo Hyorin is the best Zanpakuto for small spenders, not only has it high Reiatsu Bonus+Basespeed for Supports, it also has SWP Kenny+CSB in fortification.
Add Tenjiro+Support of Choice (I currently think of SWP Nel or SWP Toshiro or well... Kisuke) and you'd be good to go.
For pure die hard F2P, I'd kinda consider taking Zabimaru because it's gonna give you flat out dmg in Events... especially for Ryoka.