Cheap laptop bags are good for some purposes but you should consider upgrading if your needs warrant it. If you are just trying to keep your laptop from getting dusty then a cheap bag will do nicely. Personally, I have a wide variety of bags for each kind of situation. If I am going on a trip, I will select a hard laptop case with plenty of padding. You never know what may happen, especially if you fly. If you use your laptop exclusively at home and you are looking to keep it new and undamaged, pretty much any bag will do.
Most cheap laptop bags are made of ballistic nylon. If you go the cheap route, make sure that the bag has a soft insert. This is critical. If your bag does not have a smooth surface on the inside, you will create tiny scratches on the exterior of your computer. Over time, these tiny scratches will accumulate and the finish of the computer will look dull and will seriously degrade the resale value. A little caution here can save you lots of aggravation later. I know this personally because I have a laptop that looks like I rubbed it with sandpaper because of a cheap bag. You don’t want to make the same mistake, trust me.
There are advantages to having several bags to choose from. Generally, cheap laptop bags don’t bother with things like metal clips for shoulder straps, padding to prevent damage and are really flimsy. This has a side benefit. These bags usually are very light. Light weight is good. After carrying a laptop everywhere for hours, your arms can feel like they are about to fall off. So you see, although I don’t like to go cheap often, there are some advantages to having a bag that is light, especially if you are a careful person and if you are going to carry the computer all day with you. Light and cheap have their place too, just make sure you don’t drop the bag, especially if you are outside. Concrete and laptops don’t make good partners.