Regardless of price, the main question here is whether or not they would be a good feeder. The answer is yes, guppies are guppies and if you are willing to pay for fancy guppies, by all means, you can use them. The coloration is all natural, so no worries there. But only one small problem... Check to see if your LFS uses any types of chemicals on their fish. They are no good to use if they have been exposed to anything other than a stress coat or start right or similar product. Your safest bet is to buy some guppies and raise them yourself. This is time consuming, and more work than it's worth in my opinion and if anything I wOuld probably switch your snake onto something more cost effective. You may also use platies, mollies and swordtails. But only if you can find clean sources. Some stores are able to order feeder platies, check to see if it's possible!