the best way to go is with DNA testing. Start saving but since you're low income you can try and apply to DNA Detectives Kits of Kindness for an Ancestry kit. There's a waiting list but if you're on FB join their page and it will give you a boost. http://ddkitsofkindness.blogspot.com I also highly suggest joining the FB group 'DD Social'. It's DNA Detectives social site and not only are people incredibly helpful they're also generous in sharing their knowledge once you get your results. You'll also find quite a few who have found themselves in the same, or very similar, shoes you do now and are very supportive. 
Anyway, I'm an adoptee who tested at both 23andMe and Ancestry last year. I too am low income but I was in a place where I could juggle and got the kits on sale during the Summer at a great price two months apart so that helped. FWIW my husband tested recently using a kit from eBay and it was fine but you need to be careful.
I was very lucky and found my maternal side via 23andMe and my paternal side mostly on Ancestry and am now in reunion with both sides (sadly both of my parents have already died). Anyway, I suggest Ancestry first. Having the ability to attach your raw data once your results come in and create what's called a mirror tree on Ancestry can be very helpful. Once you have your raw data you can upload to other testing sites for free and you can upload it to two excellent sites to get your analysis to potential medical issues.
I'm not a DNA expert but am always willing to help especially those looking for bio parents so if you need help once you've gotten your DNA results, bookmark this, message me here and I'd be very happy to help you.
Oh and my birth last name, my bio mothers maiden name, was Johnson too. So far they seem to be in NY mostly though.
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