Is $100,000 to replace cedar deck boards with composite and address structural issues a fair price?

I am a decent DIYer and usually handle my own projects, but I've been busy and decided to hire a company to replace my cedar deck boards with composite. My deck is 1,000 sq ft. I received two bids around $100,000, which I find to be quite high, so I'm now considering doing the work myself again. The joists and the rest of the understructure are in good condition, except for a missing beam at the start of the lower deck level where there's a step down. This seems sketchy, and I've noticed a dip in the center of the deck near the house. The two companies I got quotes from suggested different solutions for this structural issue, and I'm unsure which is better. It would be difficult to dig new 4 ft deep footings under the deck here in CT, and I'm not sure if I can find a company willing to do just the footings. I'm also thinking about switching from composite to Ipe or a similar hardwood because composite gets very hot, and I don't want to deal with annual staining required for PT or cedar. I'm open to oiling Ipe. For railings, I'm considering horizontal cable railings. I'd appreciate ideas for covering the underneath of the deck beyond white lattice, and I'm also looking into installing an under-deck protection system for dry storage. I'm confused about whether to use joist tape due to conflicting opinions. Lastly, I'm wondering if there's a benefit to replacing existing posts with 6x6s or creating 4x6s by joining 2x4s.