Our company wants to resell products that change in price quickly. Our wholesaler offers a web service that we can call to get the current price of any item at any time.
We would like to call this web service before displaying the product page to the user. (It would be bad for us if we sold a bunch of memory just after a large price increase for the "before" price.)
Our ISP supports Zencart and Pinnacle Cart. The cart software should be in PHP.
If you wanted to keep compatibility with an existing store software, you could instead write an application that queries your dealer's web service for all products and then updates the store database with the prices once a day.
It would seem that if you need an up-to-the-minute price quote, you're still dealing with the time it takes for you to place an order with your dealer. I would assume you would still honor the quote given to the customer so any price difference in the favor of the customer should be 'eaten' as the cost of doing business.
Now if you really do need to offer realtime price quotes, you probably would also reserve the right to charge the going rate at the time the order is filled. In this case, the customer would anticipate that the quote and charge may differ and you can still use a daily or more frequent global price update.
What I'm basically saying is that there are inherent time intervals between placing and order and fulfilling the order that are long enough to make realtime price quotes irrelavent.