Hi.
From what you write, you will need a standalone program / script that runs periodically every 8 hours, which will download the price feed from the vendor, and then update the database of products with new prices. Some common-sense checks need to be also implemented to make sure that the new prices really belong to the products, and errors need to be flagged.
On our last project, we have implemented a page accessible both by the e-shop provider, and the customer, where they could list the items that were problematic, along with the problem that was encountered (the problems boiled down to wrongly entered product ID or discontinued product that was still listed on the client's website but not available from the vendor). This allowed problems to be solved quickly and in a transparent fashion, with minimal downtime. An e-mail summary of the update can be sent on an update as well, if you would prefer.
If you'd like to chat about the technical details of your problem, and the implementation that you require, feel free to send a message.
Thank you for reading this proposal.