Before I go into the details I’ll state that I think it’s best to purchase an Xbox 360 with a hard drive if you’re a hardcore gamer. You certainly can use one without a hard drive but you’ll be restricted on what you can do with the system. You can purchase a drive at any time but you’ll probably end up spending about the same amount that you originally saved up front anyway.
Microsoft has offered an Xbox 360 model without a hard drive for a long time. They may have been available since the system was released but since it’s been several years now I don’t remember for certain (I think they originally only came with hard drives until Microsoft added the ability to store content on external, USB storage devices). Around the holidays these systems are usually heavily promoted. Typically, they come with some form of storage, most likely just a flash drive around 4GB in size.