There are a couple of better organised B.I. product vendors - namely Pentaho and Jasper - who make B.I. product lines on top of an open-source stack; both product lines have dashboarding tools. The suites are available as open-source in some form; although they are not based on PHP they do offer web interfaces (both are based on open-source Java app server stacks) that could be controlled from a PHP application.
You may be able to get what you want from one of these packages, but the vendors are fundamentally commercial outfits. You can expect limited help with their open-source offerings unless you cross their palms with silver although there is some community support around the products. Some features are only available in their paid-only variants, so you may have to do your homework.
Some commercial options that could be a possibility are PerformancePoint, QlikView or RSInteract. Although these products are commercial and tied to a MS Windows based platform they all have a freely downloadable variant that you could use to get as far as a proof of concept. One option would be to build a prototype in one of these and then go to the business and say
"This is a commercial product that
will cost X. This is the prototype we built with the freely downloadable demo. If you want the
dashboards you'll have to come up with
the dosh to buy the kit."
Either there is a business case to buy the software or not. The entry points for production deployments of these products are all of the order of a few $10,000s, which will probably be less than the cost of developing and maintaining the dashboard anyway. Qlikview doesn't need a database server, but PerformancePoint needs SSAS (which implies SQL Server) and RSInteract needs a database server, of which SQL Server is probably the cheapest option.
All will quite happily run on a SE version of Windows Server on a cheap-ish Wintel box, although QlikView works of an in-memory data structure, so you will need a machine with a lot of RAM to run it. If you do this, look into machines that take DDR2 memory, as there is a glut of this on the market, so even server components are quite cheap. It is quite possible to get 32GB of DDR2 registered ECC memory off ebay for less than 1,000 USD.