There seem to be two main types of salon software on the market at the moment - standalone systems and online systems.
In general, the standalone systems will be more expensive, as there are often associated hardware requirements, e.g. barcode scanners, tills, touchscreens, etc. This will normally mean more initial capital outlay, or committing yourself to a hire purchase/finance agreement.
Online systems are a relatively new arrival on the salon software market, and are normally Web applications (that run in a bog standard web browser, e.g. Internet Explorer or Google Chrome) that provide salon management features such as appointment booking, stock control, marketing, etc. Often they also allow integration with a salon's website, so a client could make a booking online via the salon's website.
The business model for most online salon software is usually on a rental basis, often a monthly or annual fee, and no long contracts or tie-ins.
The main advantages of online salon software would be a generally far lower start-up cost - you would only need a bog standard computer (PC, laptop, Mac, etc) with a broadband connection and a web browser - and however much the monthly rental fee for using the software is.
Probably the main disadvantage of online salon software (to date) is that because it's predominantly web-based, it would not be so easy to integrate with hardware such as a barcode scanner - unless there was a special client application to interface with the barcode scanner that could communicate with the online software provider's server using a web service or whatever.
So I guess the main question is if the barcode scanner is 100% essential, as an online solution would probably be by far the cheaper option, at least initially.