For a 2 day Cowboy Match you will need at least 150 pistol and 150 rifle, this will allow you to shoot at least 12 stages and a couple of reshoots if required. I prefer loading on a single stage or turret press for making all my Cowboy Action ammo in .38 Spl, .44 Mag, .45ACP (Wild Bunch) & .45 Colt. I use a Lyman "T" Mag turret press with additional turrets for all required calibers. I believe in quality before quantity. The nice thing about turret presses are that you set your dies once, and once only. The ammunition that I made last year with be the same as the ammunition that I make 2 years from now. Buy a good quality press, I have been using my RCBS RS3 since 1986 and my Lyman "T" Mag since 2012. Cowboy action is addictive once you get started, so buy kit you can make large volumes of ammo, within the first 6 months or less your reloading gear will pay for itself.
You generally purchase cast lead bullets in quantities of 1,000, you may as well purchase 1,000 brass at the same time. Starline brass has the best value when buying in bulk. Plus this will allow you to have extra ammo ready in case a match comes up with short notice.