You might sneak in under your weight goal without a case. Think about getting a Power Supply locally as well. Those are the two heaviest items.
One case I looked at was 10lbs shipping and a standard PSU was was 5 lbs.
You can use that TigerDirect site to estimate prices for your parts if you can find them, or a similar item. I know there will be some extra packaging for the retail parts besides the shipping weights.
The only other trans-shipper I knew about is out of business now.