If you are registring an available domain, the cost of a domain can vary, depending on several things:

1. The TLD (like .COM, .NET, .ORG, .INFO, .ME, .MOBI) can each have different prices. A .COM is typically around $9, whereas a .INFO may only cost about $2.

2. The Registrar that you're using to regsiter the domain. GoDaddy may sometimes have cheaper prices than Moniker, for example.

3. How long the TLD has existed. During a "landrush" period (when the TLD is first created), the domain price can be signficantly higher. For example the MEXICO (.MX) TLD was recently opened using a "sliding pricing scale." For the first month of general availability the price was US$599 for a domain. But has now come down to US$24.99. This effect occurs because investors may be willing to pay more for the best domains.

4. Coupons. Always use a coupon code when registering a domain, no matter what the registrar. Search Google for "GoDaddy coupons", for example.