Ebay may well appear to be the cheapest place to start,but be careful,I was ripped off for 450 quid a couple of years ago,for a machine that had "very little use",but was obviously last used by Noah to clean the carpets on his ark.
There are bargains to be had ,but be careful,I have learned a valuable lesson.
If you are serious about starting up try to consider a new machine if your budget will allow,at least you know what you are getting.-John