Figuring out exactly what you need from a product will help to keep you from paying extra for features you don't want or getting something cheap that doesn't meet your needs. You should figure out exactly what you need the item for now, what you will likely need from it in the next year or two, and the most that you could never need in the future. Now figure about how much you are willing to spend. All of this will be your list of specifications that will be used in the next step. Don't worry about individual prices yet as long as everything is in your price range.
Many web sites have reviews of commercial products, especially computer-related products.
These reviews often list the features of different products, their prices, and how they compare with each other. The manufacturers' web sites will also contain information that will help you here. Another option is to find someone who knows about the kind of product that you're interested in and ask questions that will help you narrow down your choices. As a last resort you can always go to a local retailer and see what they have to offer. However, keep in mind that retailers want to sell what they have, so employees may be a bit biased toward what is in stock.