SkyChi, my suggestion would be to watch the engines for sale/auction on Ebay, RCU, and RCWatch. I bought mine over 2 years ago on RCO. It was advertised as bench run only. After a tank of fuel and some re-tuning it flew like a Tigre. A NIB ST 75 or 91 is almost always on Ebay, however you won't get a bargain, maybe 5 or 10 bucks cheaper than mail order retail.