Same goes for changing your own oil, or servicing your own car. If you're like most of us, (and this isn't your startup business) you [i]could[/i] figure out how to do it. But would you really be saving that much money given the time and resources you'd need?
Most webhosts run less than $20 a month for a basic package.
So for comparison:
Things you need to have your own website:
[b]A Dedicated Computer[/b] - this machine will need to run 24/7 to ensure you website is accessible at all times.
[b]Electricity[/b] - The machine will need to be powered 24/7, most machines suck about as much power as a 100w light bulb, but there is a cost.
[b]Internet Connection[/b] - depending on how much traffic your website is getting (if its a portion of your business on-line) If you're using it at home or office, you will need to make sure there is sufficient bandwidth, causing you to buy a bigger connection at some point.
[b]Static IP[/b] (or dynamic service) - You will need DNS settings to route to the machine, so you'll have to pay your provider from a Static IP or sign up for a dynamic service such as no-ip.com
[b]Domain[/b] - You need to buy a domain for your website.
Things you probably wont get if you do it yourself
[b]Usage stats[/b] - The Hosting providers keep track of this, because if you go over you alloted amount, they kindly bill you for it, but it helps you track online views.
[b]Extra protection[/b] - Most Hosing providers have firewall and DOS protection beyond what you could reasonably setup in your own home.
[b]Tech Support[/b] - Got a problem or a question, most providers have someone you can call.
I'm sure theres more and other things I'm missing. But this is a basic general assessment. I'm pretty sure you wont be able to get that set up for less than $20 a month.