When you are in the market searching for that best model for less than 100 dollars things can become tough as you will constantly find things that are much better at say 120 or 150. But 100 dollars is what you want to spend on and that can be a psychological barrier that you do not want to cross at least initially.
There are a few things that you should look for in any binoculars and that will definitely have an impact on the kind of binoculars that you are looking for. The main thing to define is the purpose of the binoculars. Define the need for the binoculars. It may be used for general field purpose or general travel or for specific type of hunting or birding. Each activity requires certain things which may not be present in the binoculars that you are trying to buy. For example in the birding binoculars the field of view should be wide whereas in the hunting binoculars the field of view may not be that important.
For binoculars which are less than the 100 dollars price point the main thing that you need to have is good image and good brightness. That will mean good lenses. A lot of binoculars are now available with Bak-4 prisms and also have fully multi coated lenses. Both these things combine to form a very good image.
The price below 100 will mean you will have to compromise on a lot of things and one of the main things among several is the design. The roof prism construction is expensive and complex to make and hence there are not a lot of options for roof prisms binoculars at this price. Even if there are some which are available at this price point then these will need to be evaluated for image quality. The best bet is to go for the porro prism binoculars. Porro prism construction is considered old fashioned but the main point here is that they will give you good quality at low price. The reason is simple as porro prism binoculars are not very complex to manufacture which translates into less costs and good quality.
Always go for the established brands because that will mean that you will have the best manufactured pieces with good optics and new technology. There are a lot of lesser known brands which are available in the market but you should avoid those if you are looking for binoculars which are less than 100 dollars.