If you’re looking for a very easy and inexpensive flower to grow, try Calliopsis tinctoria. I grow a cultivar called ‘Finest Mix’. You can get 250 seeds for less than 3 bucks at Stokes Seeds (no affiliation).
The plants grow 24-36 inches tall on cosmos-like, airy foliage. You can simply plant the seeds in the ground when the soil warms in late spring. They’ll start blooming about a month later and the show goes on for weeks and weeks.
The flowers are bright yellow with a maroon center, and the plants are happy growing in sun or part-sun.
Calliopsis tinctoria may self-seed, but not in a nuisance kind of way. I’m always excited when a few “extras” pop up each spring because they get a head start over the new plants I sprout from seed which extends the flower display.