So my current fleet consists of:

ISD x1

VSD x2

GSD x2

Raider x2

Mc-80 x1

Mc-30 x2

AF II x1

Neb B x2

CR-90 x2

Imp fighters x2

Reb fighters x2

R&V x2

I have about $100-110 store credit to spend on Armada. How should I spend it?

I play both factions and like to have options.

A second ISD, a couple more R&V for firesprays would be my suggestion for imps

A couple more AF for rebels and possibly several more CR90s for a swarm list

AFm2, neb for xi-7 and a isd

I would first look at what lists you want to run in the future and go from there. 2 ISD is very popular and powerful so I would definitely get another ISD. Many Rebel lists work well with at least 2 AF's so I would get another AF. After that just look at if you want to fly some kind of Fireball or maybe swarm with TRC's so additional R&V's and CR90's may be in order as well. Either way look at what kind of lists you want to play and go from there.

One more AFII to round out you pattern of doubles of anything not large?

Or, I say this despite being a sailor who once blew a months pay in a 48 hour liberty, unless the store credit is truly burning a hole in your pocket you might think about keeping it in reserve for wave 3.