I.  A FORM-BASED EZ-STORE with auto forms (NOT typical shopping cart -- see II and III below for that.)
Download AND EZ-STORE mockup sample or just SEE and Try It first.

GET THE WHOLE KIT OR TRY IT FIRST
(NOTE: No orders are recorded in any database with this sample)

NOTE: This This EZ-Store (above) was written in a way to be conducive to being custom-written
by another JavaScript (builder) program.  Again: This EZ-Store is basically of a NON-shopping-cart variety. It is written with max. JavaScript & the smallest amount completely-general-use PHP.

II.  For a maximum-JavaScript shopping-cart-type store and one that could be written via a JavaScript builder program: Amazingly, nothing can much improve on the 11y.o. Chapter 8 source code for the JavaScript Application Cookbook by Jerry Bradenbaugh (O'Reilly, 1999). Get the code HERE: http://oreilly.com/catalog/9781565925779 !

III.  ALL FREE: World's EASIEST 100%-PHP / mySQL Shopping Cart
(Very good, COMMERCIAL GRADE, yet very practical and easy to use!)

Here is the complete kit for the pay-by-check-and-PayPal version : Ask to receive a zip file containing the whole kit. (directions.txt, therein)

Here is the complete kit for the ssl direct credit card version : Ask to receive a zip file containing the whole kit. (directions.txt, therein)

The screenshot showing the additional directions        (EMAIL lorlarz@gmail.com to get a copy of a kit and try it.)