Well I already had the gage ( someone in my wife's family gave me a bunch of micrometers, and dept gage, and much more stuff like this, most of it is Mitutoyo, for doing some work for them). Pretty much I only had to buy the bolt. so maybe 75 cents. You can buy the dial indicator on eBay for next to nothing sometimes. They can be hard to read sometimes because the rim is somewhat different all the way around.
The more similar the rounds can be the better.
Also if you guys want good target ammo stay away from high speed ammo, the slower the better. Try to stay around 1200 fps and slower. I shoot ammo around 1070 fps (CCI Green Tag) and some others.