Affirm is very good, but if you're worried about price and easy access, I like Vitale Mo' Body Sensitive Scalp and Revlon Realistic Mild. All of them are lye relaxers.
I would never have found out about the Vitale if my mom hadn't left the top off of a brand new tub of Affirm and it all spilled out. I just refused to spend $40 again when I had just gotten that tub. Her hairdresser recommended it for her because of her scalp, and I decided to try it because my scalp had been acting funny lately. I was really impressed. It only comes in one strength, which I would say is regular so if you're used to mild you might want to speed up your application time. I still have a wave pattern (intentional) left in my hair if I airdry, but it gets straight with a roller set and there is no frizziness. No burning during application and no flat hair afterwards. I might invest in the foaming protein conditioner as my regular protein treatment.
I paid around $7.00 for everything. It also comes with a prerelaxer treatment to protect older hair.
The results from Revlon Realistic are in the same class. But I like the Affirm reconstructor better than anything I've seen from Revlon. The lye version of the Realistic used to come in a box, but I think they are phasing it out. You'll probably only see it in the tub, with the neutralizer and after relaxer treatment sold seperately.
The lye relaxers I hated were Tones and Textures and Optimum.
HTH