We've moved your topic to the hardware forum where there is better visibility to those knowledgeable with these things. I'd encourage you to register with Tech Soup so you can participate in the discussion.
What are the applications for for the products you print with the printer, are you looking for posters or banners, indoor or outdoor display?
What will be the display and storage environment of the produced piece, bright sun, shade, indoor lighting with no direct sun exposure?
What is the life expectancy of the pieces you produce, a few days, weeks, months, or years?
What volume are you expecting to produce?
HP is a maker of several wide format printers. I believe they all use an ink jet technology, but the formulation of the ink and the substrate really determines the life an application of the product produced.
Also do you really need to own the equipment or would it be more cost effective to farm out the work when you need the poster or banner sized pieces?
I know the wide format printing services are available in the US at FedEx Kinko's, Sam's club, many blue print shops, sign and poster shops, and many print shops are offering small run digital printing.
Dave