Spinning reels are available in many different price ranges, and it is not always the best idea to purchase one based on its price tag. The best way to find the best product for you is to review a variety of products, and then determine which category best suits your needs. The main categories of reels are open faced (with no gear rack), top load, spin cast, bait cast, and gravity fed. Each of these categories has its own strengths and weaknesses, so you will need to spend some time evaluating each one before you make a decision. The most important factor in determining what category a spinning reel falls into is usually the size, as most anglers have at least some preference for one size or another. This link
In addition to the size, the type of spool that the reel features will also play a role in your choice. Typically, a spinning reel with an anti-reverse feature will cost less than one with a drag system. The drag system will allow the angler to manually reverse the fishing line in order to change direction, but the disadvantage is that it can be very messy. A drag system allows the angler to reverse without needing to handle the line, making it much more hygienic and easy to use.
Once you have reviewed a variety of spinning reels, you should then consider the main categories, including open faced, top load, spin cast, bait cast, and gravity fed. If you are looking for a saltwater spinning reel, you will likely want to choose from a product that features a mono-axle, single roll ball bearings, an anti-reverse feature, and a removable or adjustable anti-reverse bearing. Saltwater reels can also feature a ball bearing or two, and some brands even offer a saltwater rated spool.