When you are looking to buy a dog bed, the price will vary according to a number of factors.
Assuming you have already identified the style of bed you are going to buy, based on your dog's sleeping style, then the two main factors influencing price are:

• Size -- a large dog bed is usually more expensive than a small one because it uses more material.
  A bed for your dog should be large enough to provide enough room for the dog to adjust and make itself comfortable in, both before and during sleep.
  Be sure to ensure this is so when you buy a bed for your dog.
  
• Material -- the price will also vary according to the type and quality of material used.
  In particular the filler material.
  For example an egg crate foam dog bed will be much cheaper than a visco elastic foam dog bed.
  This is because the latter, also called memory foam is a more expensive material and is of high enough quality to be seen as a material of choice for dogs with arthritis, dog hip dysplasia, or similar joint complaints.
  Not only is memory foam firm -- offering great joint support and comfort, it also has the ability to return to its original shape after use, giving it a durable nature.
  The above foams, are just two of several types of canine bed filler.
  Find out about them all and get one that matches your dog's needs and your own need for durability.
  If your dog is old or is one of the several breeds of larger sized dogs then it is more at risk at developing joint problems, such as arthritis and dog hip dysplasia, in which case you may wish to consider a memory or visco elastic foam bed for your dog if you are particularly concerned about your dog developing such issues.
  Consider doing some research or consulting a vet.
  

One final thing you'll want to ensure when you are looking to buy a dog bed of quality is that the dog bed cover is removable and washable or that the bed otherwise has an easy to clean surface (for example faux or synthetic leather) as a standard feature.
The bed can not last very long if you are unable to easily clean and maintain it.
Not only that, it would become a breeding ground for harmful bacteria, putting your dogs health at risk!