Your not going to want the BEST motor if your on a budget... I would personally look for something used in the for sale/trade forum. i seen a few for around 60-70$ Also look for something that is fairly inexpensive to replace parts. Ebay and this site have been nothing but good to me. The savage k4.6 is actually your best bet. If your having a huge loss of power maybe look into a new piston and sleave for it? idk just my two cents to help out a new guy. good luck