Let's first narrow it down to size. Depending on your dog size, the bed should be just a little bit bigger than your dog. He (or she) should be able to turn around easily in the bed and be comfortable when sleeping. Dog's bed should not be too small as the dog could have a hard time fitting in and would abandon the bed altogether. The right size of your dog's bed would be if you could just fit two of your dogs inside without any spare room left.
Secondly, you are presumably not looking for high priced brand name, designer signed or luxury dog beds. Also, you are looking for indoor dog bed (yes, there are outdoors dog beds too...) which is easy to clean (has removable covers) and easy to transport. Since dogs like small, warm, soft and closed places, just like the dog houses are, you should look for the bed with raised cushions on three sides - just like you sofa.
To sum it up, you are looking for a dog bed in which you could just fit two of your dogs without any spare room left, the bed should have three-side raised cushions with removable covers, the bed that is easy to transport and to clean within the price range of $50 - $75$.
Great, we just narrowed the choice down to a few hundreds, but we still have few aces in our sleeves.Next thing we will rule out is any dog bed marked with premium or high or super tag lines. These are there just for selling purpose and you can safely ignore it. Does the dog know the difference between super-premium and ordinary bed? I really doubt it. Let's just stay with the basics.
What you really should look at when buying dog bed, is bed being stain and odor resistant. Dogs can (and in many cases do) mark their bed with urine, marking it as their territory. Any time you will wash your dogs bed he (or she) will mark it again. For this you should be able to remove and wash covers and simply wash the bed with water and wipe it with paper towels. To prevent your dog from marking his (or hers) bed again and again you should train him not to.
Dog Beds - How to Find the Right One