Tim,
Why do you want an US machine anyway?
They look great in the corner of your clinic, and when you explain the 'theoretical' mechanism of action to your patient, they are deeply impressed with your knowledge and warrant paying their hard earned money for your services. If you already have one, or working in an environment which already uses it, it might be indicated, but why do you want one?
In my opinion, take the £100, and stock up on massage lotion and an ice machine. Surely that’s all you really need in your clinic?
Have a look at the following studies, which look at the efficacy of US
http://mrw.interscience.wiley.com/cochrane/clsysrev/articles/CD006368/frame.htmlhttp://ptjournal.org/cgi/content/full/81/7/1339