Hobby rocketry leader Estes Industries makes more than a dozen inexpensive launch sets (launch pad/rod, launch controller) for beginners, but their included rockets are either pre-built or not much of a challenge. For a good first build, I’d instead suggest the Quest Astra 1. Its balsa fins are mounted “through the wall,” making it easy for beginners to put them on straight. You can put it together with CA adhesive (“crazy glue”) and have it ready to fly in 15 minutes.