The cost difference is virtually non-existant. However, headstamped 7x30 Waters brass is more costly, and getting hard to find. I make all mine from 30-30 brass. Nothing to it, you just lube the case and run it up into the die. Then you load a very light load for the first fire-forming and presto, you have a 7x30 Waters. The fire-forming actually moves the neck forward and expands the case walls out a little.
I've also heard of some folks putting a tiny charge of Bullseye pistol powder (3 or 4 grains) and stuffing the case with tissue on top of the charge, then filling the case with grits or cream of wheat, followed by another wad of tissue to fire-form the case. Always sounded like a lot of trouble to me, but it would save a lot of bullets if you want to be frugal.
I usually just use my first fire-form loads for target practice. I load 5 grains of Red Dot (shotgun powder) with a cast lead bullet for the fire-form/target practice loads. Surprisingly accurate.
A Dillon 550, huh? Those are great presses, but not too good for a beginner. A lot of crap to adjust if you change dies to another caliber. You might consider getting a very basic single stage press like the Lee Classic to learn on. Save the Dillon for later. I've been reloading all my 41-year-old life and still prefer a single stage press for my rifle loads.
