Need info about Aprilaire whole-house humidifier (water panel) filter
 

I have 2 whole-house Aprilaire 550 humidifiers. I need to replace the
water panel filter (?) in both. On opening the cover, I saw that the
filter looks like its a hard wire mesh kind of thing.
Is this the water panel filter I need to replace? Online prices range
from $8-15.
There is a plastic frame that this sits in. Does this need to be
replaced too, or just the mesh filter part?
Thanks.
Mark Sabatini