So I spent all I had on gear, after selling random leftovers I expect to have 250ish fg for charms..
I'll never afford full inv of 3/20/20s (also I'm on ladder where those almost never exist)
So what stats can I afford for use on guided/multi bowazon?

10max/ar/ life or frw

Or just even clean 9-10max/ar

as above, grand charms.

If not using ignore target's defense or guided arrow exclusively, attack rating and damage charms for softcore, life and resist charms for hardcore.

At least on non ladder you can use the search feature and search for "frw", "3frw", "5frw" etc. and you can always find really good deals on frw charms. If you see someone selling a 3max/17ar/3frw and that's the only item for sale in the thread it'll be expensive because they know what they have. What you want to do is find those people listing dozens of items in one thread or a mule cleanout type of thread. I've funded my entire inventory by doing this and I have gotten some ridiculously cheap charms. Large charms really seem to go for cheap in those threads. I got a 6max/42ar/5frw large charm the other day for significantly less than one single 3/20/3 goes for and all it cost me was 2 frw.