OK, to be realistic, in IT, there isn't that much you can actually do legally, so a wind tunnel is way down the list of priorities.
But the air dam is free, so I guess the question becomes, what do you want your airdam to do?
I'd submit that you want it to lower drag, provide effective air management for brake, oil and water cooling, and provide reasonable downforce.
Well some of those things can be monitored very cheaply, and others can be deduced from instrumented testing.
There are of course, books written on the subject, but for a real guy/real world example, try going here.
http://forums.pelicanparts.com/showthread....20&pagenumber=1
It's a long thread, but there are lots of real world tuning and testing ideas. Jack is nothing if not industrious. And to do this sort of thing you have to be. I bet the cost to create an accurate scale model, and then rent a wind tunnel will be nearly a 100K when it's all said and done.
CFD consulting would be significantly less, but still very expensive.
One final idea would be to find a student who is interested in racing, and is in an engineering program and strike up a friendship. Of course, thats a lot different than hiring someone, but if he's not tooo tied up with his girfriend pursuit, his partying and his classwork, he might fit you in, LOL.