I read an interesting article awhile back about this exact topic, and I actually found it again online. Hopefully the link works, its at
http://www.msnbc.msn.com/id/10810970/
Hope the article gives you a little more insight on the world of allergies.
You can have Zoey tested for allergies, but the prices I have heard range all over the place from $60-$350.
Maybe others can give better estimates on the price. You can also contact your local vet to see how much they charge for a procedure like that.
Good luck!