Is $25,000 to replace the whole shower a fair price?

I bought a home without thoroughly looking at the shower. I noticed dark brown/black stains on the caulking during inspection, which the inspector thought was mildew. We got it tested, and the results said 'could be mold'. I've tried cleaning the caulking many times with various products, but it never fully came clean. After using hypochlorous acid and an electric scrubber, I found that the caulking is cracked or missing in many places. I'm worried this indicates a mold problem coming from the subfloor. I'm a first-time homeowner and have no experience with this, having lived mostly in military barracks before. I have anxiety and a tendency to spiral, and I'm concerned my husband will think I'm overreacting if I suggest replacing the whole shower based only on my opinion.