Hi Alison,
I can give you some pretty good feedback on this. I actually had transplant surgery when I was 28. Long story short, the transplanted hairs grew, but the hairs around them continued to fall out. So 4 years later I had to start wearing a hair system anyway. It's not that it didn't "work" per se, but most women with diffused hair loss will never be able to achieve the density they want to with transplants. They get coverage, yes, but it will almost always look thin as the remaining hair continues to fall out. 
That said, you said you have alopecia areata, not diffused loss, but unless you have consistent spots, I do think it would be hard to chase the bald spots with transplants. Since AA is an autoimmune disease and therefore unpredictable, it might be really expensive and frustrating for you. 
Also, I agree that 28 is young for transplants, in hindsight. You don't really know what your hair is going to do yet and if you are a good candidate for it working well or not. I wish they had told me that at Bosley. It's kind of like getting Lasik too young before your eyes are mostly done changing. You end up having to get it again or wearing glasses anyway.
Good luck with your research. I hope you find a good solution that works for you! 