I think you'll find pressure treated wood decks at $15-20 sq ft, especially at that height.
Just me, but some, most, well all, PT wood is junk when used for decking/railing material. Except maybe the the KDAT (kiln dried after treatment) stuff .
We used Timbertech XLM decking for ours and its held up very well. It runs about $3.65 for a 6" wide linear foot for the decking ,,,, and that's w/o the hidden fasteners

But it comes in 20' lengths and can be a very clean looking installation.
Frank