I have 2B-2Cish hair, I think and it's very thick and frizzy in the back.
What I use is my Ultra CHI iron when I want a sleek and shiny look. I also use the CHI silk infusion, which is a little pricey, but I think it's worth it since you don't need a lot.
Another thing is your technique also plays a big role. I see some girls just grab a chunk of their hair and straighten, but their hair may still look bumpy in some places. (Heck, I used to do that.)
The comb-chase method is very helpful. Also, be sure to grab small sections. This might eat up some time, but if you want a straighter and sleeker result, it's definitely worth it.
I got my CHI when it was 120$, which I regret, because Ulta had a sale, 6 months later, and the Ultra CHI was priced for 99$, including the heat mat and a small bottle of the silk infusion.
You can check Folica.com for their flat irons. They usually have sales and promo codes so you can save money.
I bought my Solia flat iron there for only 55$, and that included shipping. I use my Solia to straighten my bangs, since it has temperature dial, therefore less damage to my bangs if I were to use my CHI.
Before and After with Ultra CHI iron:
(The same day as above, after biking 15 miles in the hot sun, sweating my face off)