Php site + shopping cart

Hi guys,

I want to create an online shopping cart, one problem aint got a clue how 2!!

I can build a php/msql dynamic site no problem, but I want to know if anyone knows a good cost-effective way to integrate a shopping cart to a dynamic site?

Basically I want to design and code as usual then integrate cart, any ideas?

Your help will be much appreciated!

W Digital