What will a Canadian Non resident over 183 day have to pay?

I'm a Canadain living in Canada, working in Texas for and America firm as a Consultant. I'm on a TN visa.
I'm getting close to my 183 days and was wondering how I'll be taxed? How much more taxes will I have to pay if I exceed 183 days?
Should I just quite or take a leave? I'm not willing to take a 20-30K hit for working over my limit!
Also can anyone refer me to a better US/CND tax accountant?
Thanks,
Dean

See me at forums.serbinski.com, I answer these Q's there