The cost for these services.Let's examine these one by one...
Web Servers
Web serving machines come in all shapes and sizes with a multitude of configurations and manufacturers, but basically they are a computer not unlike the one before you right now. They have a processor for performing tasks, a hard drive for storing files, and an operating system used to run the whole show. Processors and hard drives use numbers to describe the size and speed of their operation, and as a general rule, bigger is better. Operating systems come in flavors that you may or may not have heard of... Linux, Windows, Macintosh, and Solaris are the most popular.
Network Connections
How your web server connects to the internet is probably the single most important factor of whether or not you will be happy with the performance of your web site.
Supporting Documentation
Does your web hosting company have a large published library of information on how to do the things you need to do to manage your website? Are there message boards where you can ask questions and learn from others both directly and indirectly? Or do you get 24 hour phone support with an endless menu directory and when you finally get a real live person they ask you for a ticket number that you don't have and won't talk to you unless you do?
Cost
Costs vary widely based upon all of these things... Remember, you truly do get what you pay for in a web hosting company!