Shopping cart software - New Designer

[pghdesigner]

I'm a fairly new web designer that has never worked with shopping carts. This man is contracting some freelance designers and he really likes my designs so I have a good chance at the job, but some of the sites he needs he wants a shopping cart included.

Is there any software out there that's good to use when building a shopping cart for HTML sites that's not insanely expensive? I'd like some of your opinions on them instead of me taking a chance!

Thanks!