What engine are you running? Of course racing tires don't last much when I am on my 50s hp Wankel (Aixro XR50) or on my KZ shifter Modena engine (hp on 50s too), but they do last a long time if have the right setup with 100 cc reed/rotary engines and much more with Yamaha KT100s. If you go to a National sprint race you can even get free used tires from some many drivers who left them at the track after just a few laps. They will be more than good enough for practice, or some might sell them to you for very low prices.