Welcome back and Happy Holidays!
This could be the part of the famous and ongoing "scratch vs. mix" debate. Everybody has their own opinions. There are those that say scratch is the best way to go. They're right. There are those that say doctored mixes are the way to go....they're right also. Hmmmm...... it is a puzzlement.
You said: "Nothing is wrong with the method Im using but Im wondering if it's cheaper to do scratch."
If nothing is wrong, why are you looking for a solution?
"Is it really cheaper or better to do scratch vs mix?"
Cost: Depends on your ingredients. Whether or not it's "better" is up to you. If you are "ashamed to admit" that you use a box mix, then don't share your recipe. Personally, I don't see a problem. If the customer/recipient likes the taste and texture, who cares?
How can I make it moist like duncan hines?
Duncan Hines (and other mixes) are able to commercially incorporate emulsifiers that help the dry and wet ingredients "bind" together. Here's an excellent article by Anne Byrn, author of the Cake Mix Doctor:
"What's in a Cake Mix?"
Scratch bakers do the same, but exceptional scratch baking requires practice and science and more practice, until you know all the variables that can occur with ingredients, temperature of ingredients, weather, altitude, etc.
I am a hobby baker and have a few scratch recipes that are very good. I prefer to doctor mixes. It's easier, cheaper and I can keep shelf-stable ingredients on hand, reducing trips to the store for ingredients. Granted, everyone who tastes my cakes gets that taste for free (lol), but I haven't had anyone ask if it's scratch or mix.