Extra Shipping Fee for Specific product unless over a certain $ amount.

[PointTwo]

Hello!
This is my first time posting, so hopefully I am not wasting anyone's time, but through extensive google searching and searching these forums, I have come up with no solution.
I am using VirtueMart 2.02.  Joomla 1.7.0.

I have several products for which the shipping is set at a flat rate of 9.99, unless the amount is over $250, in which case it is free.  However, I have one product which contains CO2 which is more expensive to ship.  The flat rate for shipping needs to be $30 for unlimited quantity up to $250 worth of the product (it's $30 each), at which time it becomes free.  I can not for the life of me find a plugin that allows me to isolate this product from the others, while still applying the free shipping over $250 rule.  If someone orders another product with this one and the total is under $250, the shipping could be $30.  But not $9.99 as its showing now.

The site is www.pointtwousa.com.

Any suggestions would be greatly appreciated, and if this has been discussed before, I apologize for not finding it and please refer me there.
Thank you!

[PRO]

what plugins have you tried?