I'm one of those allergic to EVERYTHING kids. I found out I was allergic to milk when I was about 10 years old. Considering my mom was raised on a farm...and my dad, bro, and sis weren't allergic to it... I never really eliminated it. I remember mom bringing home rice milk and making me drink that... I haven't tried it since, but I remember that stuff being disgusting (then again...I was 10 and way less open to food possiblities). Basically I never drink milk or eat ice cream, but would eat cheese and yogurt and chocolate...haha. Then I would get hives, and really bad tummy aches. I swear since I was a little kid I've just been a walking hive.
I also get kidney stones a lot...so I met with a kidney doc and he told me I couldn't have spinach, soy, chocolate or any foods high in oxalate or calcium. When you add my dairy allergy...I seriously can not eat much. It sucks.
Now though my doctor has been having lots of tests done for me. My face had this really bad, blistery reaction this summer. She did a patch test and found out I'm allergic to 3 main preservatives found in most cosmetics/household supplies... I even have to change my contact solution and toothpaste! She has me getting extensive food allergy testing next week. I'm nervous my list is going to be as long as your sons
...
do you have a health store...like a co-op or veg*n friendly store nearby? I've learned that the employees that work there are a wealth of information. They've helped me quite a bit! Actually...making an appointment with a dietitian or nutritionist would be a good thing for your son. I bet you can even get a referral to help with the insurance costs.
Have you tried cous cous? That's a pretty versatile food...I do a lot with that.