Is $40,000 to add a cover to a 12x12 deck a fair price?

I am a new homeowner with an existing 12x12 deck. The previous owners added a second and third level to it on two sides, and the railings are 4x4 posts mounted against the joists on the edge. The deck's legs are currently supported by various paver blocks, and I've added three supports underneath the main portion for stability. My backyard receives a lot of direct sun in the late afternoon, and I want to add a cover. I'm considering a DIY aluminum cover due to concerns about the pavers' weight capacity. I'm also unsure if I can mount a cover on top of the existing 4x4 railings or if I need to remove them and build new ones.