Going completely gluten-free does a lot for my skin. I've never had cystic acne, but I used to get annoying hormonal breakouts on my jaw, chin and neck. I played around a lot with different factors, like sugar, dairy, etc, and what I discovered is that gluten has a gigantic effect. I'm completely off it now, but on very rare occasions I'll cheat, and when I do, I just know I can expect a breakout within a week. And it happens like clockwork.
Cutting out gluten also vastly reduced my PMS symptoms, to the point where I have to look at a calendar to know when my period is coming or it'll surprise me.
Echoing what others have said about expensive skincare--the best routine I've found is coconut oil to cleanse and moisturize daily, with a light salicylic acid cleanse or enzyme mask (Alba makes one I love) every few days. And otherwise, I just let it be. However, I'm not a big makeup wearer. (But when I do wear it, there's nothing better than coconut oil for getting it off!)