How much should a corporate buyer expect to pay for professional event photography? Like most things in life, it depends.
I recently polled photographers in a variety of markets (large city, medium city, smaller towns) and the average hourly rate ranged from $150-$200 per hour. For this rate, a corporate buyer can expect the photographer to dress appropriately for the event (no shorts and t-shirts for a formal setting), arrive early to scout the venue and make contact with the client to ensure that any details or questions are addressed, bring sufficient camera and lighting equipment and backups in case of malfunction, and interact courteously and respectfully with the event guests/participants. And, of course, create images to the buyer's satisfaction.
After the event, the buyer will likely receive high-resolution JPEG files on a disc or online gallery with license terms that will have been negotiated prior to the job. Licensing enables the creator (in this case, the photographer) to retain ownership ("copyright") of the content and gives the client the rights to use the images in certain ways. The images for some events, like a cocktail party, can have a very limited shelf life so you may receive an unlimited usage license for these types of photographs. If the images have more lasting value, the photographer will negotiate terms appropriate to the nature of the photographs. In this case be prepared to pay more for the licensing. If you need prints, you'll want to indicate that before the event so the photographer can include that in his estimate. Note that license fees may be added in addition to the hourly rate established for the photographer to work at your event.
Events can't be repeated if you don't get the right person to photograph your job. Don't hire on price alone--take the time to get estimates from pros and hire the one whose capabilities best fit your needs.