I've been doing some do it yourself plumbing on our kitchen sink for the last couple of months. The sink had a Price Pfister single handle faucet that has been a little leaky and loose since it was new 10 years ago or so.
I replaced the cartridge, which I had to order online since they don't carry them locally. Then the hot water shutoff valve. Then the hot water supply line. Today I replaced the whole kit and kaboodle with a new faucet and supply lines.
Working under that sink I can understand why plumbers charge so much. Real life home repairs and improvement projects can be a frustrating experience. In the real world pipe fittings corrode, old pieces break and access can be a challenge - unlike the ideal world you often see on shows like Hometime, This Old House, BobVila, and New Yankee Workshop.
Putting in the new faucet took a couple of hours and two trips to Lowes. Taking out the old faucet took about twice as long because a nut had corroded and was frozen and it was impossible to loosen the spray faucet nut by hand (thank goodness for Vice Grips). They usually skip the prep work on the DIY shows because it's just boring grunt type work. Although when it comes to plumbing if you aren't careful you can break a solder joint beneath the floor or accidently do other fairly disasterous type things.
Those armored flexible supply lines are a life saver for do it yourself work. I'm not too keen on using a blow torch and solder in a good location let alone under a sink near electrical wire and in the basement near nice dry wood beams.
If I was a plumber, electrician or carpenter I'd like to work on new construction rather than any kind of remodel/repair stuff. As a homeowner I'll do that work on my home whenever possible - but you couldn't pay me enough to do it - partly because I'm so slow and partly because if I accidently break a pipe under your floor or start your house on fire with a blow torch - the cost might be prohibitively expensive.
Better to hire a union plumber, electrician or a real carpenter.