An older Apex should be a fine set up. I would also look at a Conquest 2 or a Conquest 3. You will be able to pick up a used C2 or C3 cheaper than an Apex. The C2 and C3 will also be longer axle to axle than an Apex. Good luck with what ever you decided to shoot. There are a couple of websites out there like 3dshoots.com or AT which has a 3D section. If you have questions just ask them here on TBH and you will probably get a better response.

Depending on the shoot, you should be able to use your hunting rig, and stay in a hunter class. For ASA you might want to pick the hunter novice class. Closer shots and it was actually intended for beginners to let them get used to how 3D is played. IBO would also be Hunter class, but i have noticed a lot of folks in that class shooting hopped up hunting rigs. TFAA/NFAA has the Bowhunter, and Bowhunter Freestyle classes, and each has different equipment restrictions. Check out the web sites for each org. and see what best fits your desires. The bows aggie suggested are really good shooters, as is the Apex. Used conquest2 bows in target colors are about $250ish. Archery talk had a classified section dedicated to target bows, and you should look around in there. Lotsa good deals to be had from good folks. Good Luck in your search, and hopefully we will cross paths on the range someday.

Joining Salt Grass - great decision. You couldn't ask for a finer club in south Texas.

When you say "older" bow - don't get too old. You can get great used bows that are 3-5 years old for about $250 fully rigged. If not rigged, plan on $100 for rest, sight, and peep. And don't forget the release. You can also get a new Reflex and Jennings for close to the same price. They are the cheap brands of Hoyt and Mathews (I think Jennings is anyway.)