The local style 1 day matches i've been to its been $20 to enter. Additional cost are 1 hour drive, ammo that you shoot. Normally say 50 - shot, 50 - 9mm, 50 - 5.56. Don't miss and its cheaper
Gear wise I run a cheap Glock 17 I got that was well used, $600 dollar ar I put together(as in upper pinned to lower), and saiga I converted. Most of the time you can put extra mags in your pockets. Other times if you need more just what ever cheap holders you can find. I have a good holster for my pistol, you don't want it falling out and getting you disqualified for the match. For the AR and saiga I have a $20 mag holder.
You don't need to practice shooting to go to matches. You don't need to hand load, factory rounds work fine. Everything is up to what you want to spend, what you want to do.
You don't even want to know what "People deeply involved" in the sport spend. It would make you not want to try.
3 gun is fun!! Best rush this side of racing that I've found besides alone time with your special lady.