This cage retails for $350+ new, I have a line on one that I can buy used for less than $100. It is powder coated, so I think it will withstand water well enough. Though, if that chips, which hopefully wouldn't happen, the cancer is sure to set in. A lot of bird enthusiasts are using misters, like the mist king, these days. I think the bird industry is working towards that marketability in larger/nicer cages like the one in the OP.
The dimensions seem ideal, its 24w X 22d X 65h. It's on casters for easy transport. It has drawers for easy clean-up...top and bottom.
On a side note...do house windows block UVb rays?
It sounds like your mind is already made up about this because you've dismissed everything everyone has offered as advice. Not that there's anything wrong with that if it's what you want to do.
For what it's worth, here's some more advice. Bird cages can work, my first cham came from someone else in a bird cage. I found it difficult to feed even crickets because even with a cup if the crickets got out (which they always managed to do) then they were everywhere in no time. Anything besides crickets and meal/super worms were out of the question because any worm with sticky feet could just crawl right out. (I don't touch roaches.) It's easier to keep up humidity in the screen cages. And even well made bird cages DO rust. Takes a while because they're coated, but with the amount of water used for chams it does happen.
It might take some adjustments and adapting on your part to make it work. Also if you take a look around some of the pictures posted on here some of the screen cage setups are just gorgeous - look like a true rainforest. I think they're prettier than any of the bird cage setups I've seen. Horizontal branches are not the only option. I wire the bendy branches to the screen and can make awesome setups without any unsightly restraints.
And no, glass and even plastic do not allow UVB to pass through. You have to have adequate UVB for your cham to be healthy.