Filling a cupcake can be done in so many ways. I love to invent and bake cupcakes with various fillings. I've done both piping and scooping to put the filling inside the cake and I prefer the piping method, in which the cupcake is injected with a filling. It's more consistent and cleaner. however, it completely depends on the type of filling be used and the type of cupcake being filled. Either way, it's majorly labor intensive. I'm guessing that's why the price difference is so large.
Regardless, if you're going to charge that high of a price, then at least make it consistent. Cheers.