For Panther Product, they are actually aluminium mesh so the whole thing is rust free.
I have installed their Premium series, mainly for asthetics and natural cooling consideration.

In short 3X7 door roughly 3k
(3x7) x2 panels sliding door 6k
(3x7) x3 panels folding door 11k
and that is with a 20% discount. Their standard product only give 10% discount.