Paul,
My wife, who is a qualified accountant, taught me all about the cost triangle. The three sides are MONEY, TIME and QUALITY. Once you fix one parameter the other two are inversely proportional. So if you have a tight budget be prepared to put some time into making a machine capable of the quality you want. A lot of that time will be researching the best design, probably a fixed gantry as Jazz suggested, and how you will construct it which depends on the facilities and skills you already have.
You won't be short of advice on this forum! Just keep asking the questions.