on my site cheapstairparts.com go to wood products then handrails and i have only 1 product listed.

here is my problem

shipping will cost an extra $25 packaging if they order 1 to 4 of them. because our special packaging cost $25.

if they order up to 8 thats $50 extra.

but how do I incorporate this into my system. I can't add a flat $25 per item because if they order 4 it makes it $100 extra.

How do I do this?