I have been getting the keratin treatment twice a year for the last couple of years. Before that, I used to get a more traditional relaxer, but I can't remember the name of it.
I love the keratin treatment. My hair is 1000x better than it used to be. I can still wear it curly if I want, but it is much easier to straighten too. My big problem is frizziness and that is where the keratin has really made a difference.
My stylist gives me a good deal on the keratin, so I am not sure about the cost normally.
Also, I have seen an Aveda treatment mentioned on here that is supposed to be safer than the keratin. So, you might want to look into that one too.
I get the Coppola one done. My friend is my hairdresser and charges me $75 for an "express" treatment, which I think is the same product as the regular treatment but she doesn't flatiron it in as small of sections or something. It doesn't sting my eyes/nose/throat like I hear some brands can. My blowdrying time has gone from 30-40mins to about 15, but I also bought a professional grade dryer so I'm sure that has something to do with it as well.
The thing I love most about it is that when I fix my hair, it stays that way. No more getting frizzball when I walk outside on a humid day. The keratin also helps it hold curl longer when I roll it.