I would have a look at what suppliers have. Some have used machines for sale, and may offer a short term guarantee. Other sell machines on for operators that have purchased new from them.
The main guts of a machine are the vacs, pump and heater elements and these are the items that will eventually need replacing, so if buying second hand, it may be a good idea to keep enough money to one side just in case. Say £1,600 for machine and £400 standby.
Dave.