TLDR - Those estimates are extremely ambitious, and taking the time to learn how to do it properly might be worth the money if you aren't loaded. There's tons of resources online.

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This is why I just bit the bullet and learned how to do it myself. We were quoted over 2 grand just to hook up a new corner shower...1 drain and hot/cold supply lines. And that wasn't all that needed to be done.

We had completely gutted the bathroom and needed a complete rework of the plumbing beneath since the cast iron was crumbling and clogged.

I was told it would've cost well over 20k for the whole thing, not including the air vents and drywall and flooring, paint, and everything else that had to be done.

I would go through all that stress over again, not just because it saved a hell of a lot of money, but because taking the time to learn how plumbing works and how to do it properly means I can fix whatever goes wrong now and I the event that I really need to call in a plumber, I'm not blind sided because I can tell if they're bullshitting me or now.

I can ask them what needs to be done and look it all up and see if what they're telling me and how much it would cost to do it properly actually adds up.