If you are putting goldfish or koi in your pond, you will need a pump. Going to the nearest big box store for a pump will get you a cheap one, for now. Over the year, if it lasts that long, it will cost you more in electricity than the pump cost you. As a general rule, the cheaper the pump, the more expensive it is to run.
I have found after almost 20 years of buying pumps that it pays to buy from a recognized pond supply store and buy a recognized brand name. Quality pays and it will pay you in the long run to get a good pump. I have stocked the brand names that I have used and depend on. The last thing I wanted was a customer calling me to say his pump had failed and his fish were dead. So I soon learned what brands I could count on and which ones I could not.