If you own a club, and have consistant business (say 20+ per week), then I think you may need to raise your budget a bit higher. The higher quality crank (or electric) machines tend to be over that price range, especially if you need a stand. If the club is small, and business say is no more than 15 per week, then int. level crank might be the answer. I believe HQ string machine (w/ stand) is around that price range, but you may need to factor in S&H cost.
Also, if you never string a racket, I will not recommand you work on customer's racket right aways, regardless how good your machine is. You need to have enough practice (say 20-50 rackets for my standard) on some old rackets / strings, before handling any real deal. This forum have a lot of good information, and youtube can be a place to search. The key is the hands-on practice, after you understand the concept.