Whoa. One thing at a time.
First the vanity (counter/sink)
The cheapest way to do this is to buy a kit at the home center. They will sell a top, base cabinet and faucet in one box you can put in. It wnt go wall to wal as you now have. I'm guessing a kit may be about $200 - $500 for everything. I don't see the kits online, they are usually an in-store special buy.
As for the shower - Thats more involved. A one piece is more involved that screwing it in and adding doors. Those screws go behind the drywall.
I suggest you do one thing at a time. Replacing the vanity should be pretty easy. Don't go crazy gutting the bathroom like they do on TV. Just carefully remove the old counter, sink, etc and put in the new. If you do that without too much headache, time, frustration, etc then we can help you with the shower.
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