The more economical kind are simply birdseed sunflowers. Take an ordinary bag of sunflower seeds intended for the birds, and plant some after soaking a short time. A large fraction will bloom, in my experience. The flowers I've been getting are not very large or tall, but there's a lot of them and they're very easy for the lazy gardener.
A little more pricey, but definitely worth it, are the showy Russian Giant sunflowers you can get at almost any seed rack. Nearly all of them germinated for me, and the results were spectacular: blooms as big as my head and nearly as tall. These at quiet spectacular and definitely worth a couple of dollars, if you have a large enough pot. I repurposed bamboo for support where needed, sometimes tying with last year's stalks for added reusiness. I'm hoping to plant enough this year to shade a south-facing wall on the roof of our building and see if it helps reduce the heat.
Not recommended: dry-roasted salted sunflower seeds.