When pricing replacements for these, I discovered that the average price for these two pieces of cheap plastic is about $120.  

how much should it cost to rip out a steel tub, plastic wall surround, and replace it with those plastic, 3/4 piece, acrylic tub and surround I see at Home Depot for about $300?

If you do take it down yourself, make sure the place is well ventilated (open windows), the ceiling is sprayed to minimize dust, you wear a respirator/mask and safety glasses and you block off the rooms that don't have the popcorn ceiling with plastic.

It also costs more for the deleading if there is furniture and belongings there as we have to move everything into the center of the room and seal it in plastic before we begin work, adding labor and extra material costs to the job.That being said, I can check the address for you to see if its ever been inspected for lead.

I have plastic opaque blue business cards.

But hey if you have a coin laundry, whats few feet more plastic pipe.

In the meantime I am getting a wild range of insane quotes (like 10% of the price of the house) for what it looks like partially replacing old pipes with plastic PVC ones, and then deal with remodeling and re flooring These guys must make more money than The Wolf Of Wall Street!

I'm talking new roof, new HVAC and duct work, new electrical panel, new paint, new PVC & PEX piping throughout the house, new doors, some new windows, landscaping and gravel is all fresh, new plastic in the crawl space, new outlets and switches throughout ... new garage door, roof, and paint on the single detached garage which matches the house. 

Steel will have to battle, staplers, lawn mowers and plastic tubs, to get on a ship and get unloaded and distributed.This is a solid location from both a Customer and a competition standpoint, so we can take on the additional costs. 

The dirt compaction and consistency of dirt type are the major contributors to cracking.Floor Sweating: use clear plastic underneath pour.Heat/Cooled building--Vapor barrier for floor to help keep sweating/humidity down.