MEGARMS
KnowNothing
Equipment requirements are in large part the reason that 3 Gun is not as popular as IDPA, USPSA, and Steel Challenge. All 3 gun shooters started out with just a rifle and a pistol. It can be very intimidating as well as confusing. I remember my first time I brought my Remington 1187 field shotgun with a 5 round capacity. I shot it one time and then borrowed someone else's.
My recommendation would be to register, bring your rifle, pistol, and mag pouches that you have as well as some shotgun shells. I will help you find someone on your squad who would be more than happy to share their shotgun with you. In fact, I don't recommend buying much gear, especially a shotgun, until you have spent some time talking to the guys on your squad about what they run, what they used to run, and why they don't run it anymore. This goes for shotguns, gun belts, holsters, pistol mag pouches, rifle mag pouches, shotguns, and just about everything else. I wish I would have had someone give me this advice as it would have literally saved me hundreds of dollars (actually closer to $1500).
I forgot to add the most important part of all of this. Shooting 3 Gun is like mainlining heroin. The addiction will set in almost immediately and your cravings for more will be untenable. It will cause you start lying to your family and if necessary you may even steal from them in order to support your habit. You will toss your golf clubs in the trash and your friends will soon start asking why you no longer come around. You will try to explain your condition to them, and even try to get them to try it too, however if they have never felt the burn for themselves, then they will soon fade away. It will make no matter to you because all that is important is that you are on a group text with 10 other addicts, discussing which ear and eye pro are the best, and how you can find a match that is less than 3 hours away from your home.
In other words, the initial investment in 3 Gun is worth it and it is a buy once, cry once game. Show up, shoot with us, and I promise you will come back for more.