I reckon that the cheapest PCP would probably be a Chinese made "78" CO2 rifles that has a filler cap fitted to the cylinder end so that it can be used with compressed air. The only problem, is that the rifles need work done to them .....so first you need to know what you're doing. A polite summary, is that they are basic and have limitations. I use one as a fun rifle in the woods behind my house. Can be pushed to 35ftIb in .22 (max of 5 shots) but have mine set far lower for more shots. It works and its cheap.