Website hosting is typically measured in the amount of disk space you're allotted on the server and the amount of data transfer or "bandwidth" you need for accessing the server. For example, if you have a lot of customer interaction at your website, such as files to download, you will access the server frequently and you'll need more Web hosting transfer space than someone who simply puts readable text on their website. The more "items" or "content" you have on your site (i.e., photos, maps, PDF files, etc.), the more disk space you'll need for website hosting.
Many services offer a low "starting price," but require you to prepay for two or three years of service to get that price. After the promotional period, the renewal price for some services can be two, three, or even four times the initial promotional pricing. While the initial deal might be incredible, the cost of transferring your site (or paying the added fee) in a couple of years may be something to consider.