You can save a lot of money, and avoid a lot of workmen ripping you off and tramping dirt into your house, by doing certain things on your own. And you can also save yourself the time and hassle of tramping all over town to get the stuff to do-it-yourself, by ordering online.
Take sinks. You can install stainless steel sinks yourself into your house. How do I know you can do it? Because I can do it, and I'm the second most unhandy guy ever. (The first most? That Jeopardy! contestant who hit himself in the back of the head with a hammer. How'd he get on the show and I didn't? And why would you tell people that story?)
I installed my own kitchen sink not long ago. To do that, I had to go and drive all over town to those big-box stores, wander through one until I found the sink section (helpfully hidden behind "Christmas decorations") and then try to decide what sink to get, then wait in line, then haul it back home, then put it in -- and I wasted about 1 or 2 hours doing all that, so a job that could have been done in the morning took all day.
Here's what I should have done: order my stainless steel sink online from Shop Sinks and Faucets, a BBB-accredited online sink and accessory seller. They sell their own brand of sinks, made to the high quality you expect, but with lower prices than many competitors because they don't have to mark them up to pay the manufacturer AND themselves. Then, the sink gets shipped to me and I install it and I'm DONE. And can go back to watching Jeopardy!