What many learn is that such is best done at Kinko's or other. It always beat out 500 sheet costs for me.
To curb costs, go laser. http://h10010.www1.hp.com/wwpc/pscmisc/vac/us/product_pdfs/500083.pdf notes up to 52 lb paper.
We've recently started doing advertising for the services we offer in our company. We making the ads mostly in Adobe Photoshop or Microsoft Publisher... there are text and images on the ads. The Photoshop ads we do are typically 600 DPI and look very good at that resolution, so I don't think we need anything that is printing substantially higher than that.
We will print mostly on 8.5"x11" sheets w/ 40 lbs stock paper but may also have the need to do smaller postcards.
We should not be doing more than 5,000 pages a month. We we do print, we will likely do 500 pages at a time and would like to do minimul babysitting (which is a problem now with our current printers, we are constantly monitoring for paper jams or having to feed in more paper).
In a nutshell, we need something with good print quality, moderate speed, and that doesn't require a lot of user intervention. It must also have a network interface, but I figure just about all of them do nowadays. We are limited to $7,000 to spend on printer and accessorries, but realistically I think we can do this for under $4,000 and still get something very good.
Some of the offerings from HP look good (such as the 4600 or 3800) but I have no idea how they compare qualitywise to offerings by other manufactuers.