You'll save yourself some significant time, by picking up a quality product already available and adding some custom elements yourself. Maxibloom is around $15usd for 2.2lbs (1Kilo) and is a great "general base" to start with. I hear Jack's is pretty dang good as well. They're both "Mixes of powders" the companies buy in huge bulk.
The only way your "mix" is going to be cheaper than buying off the shelf, is if your time is worth very little.
Sticking with "Improving Something Readily Available" is a much better use of your time.