Go to your favorite shopping search engine to search for "Microsoft Office 2007 Student PC" (add the "PC" so you don't get books in your results) and you'll receive prices ranging from as little as $73 upward to $197. Considering Microsoft reports a price of $149.95, you know that the $197 price tag is outrageous. Remember to verify the number of licenses and the edition when checking prices.
The $73 price doesn't exist. Search results are imperfect or they have old information. Maybe it was $73 in an online auction that has since ended. The cheapest price from a store as of this writing is $79.99, but going to the store reveals it retails for $89.99. Maybe they had a sale and the sale ended or sometimes the search engines don't receive the right information.
Don't automatically buy the cheapest one. You don't want an illegal copy, do you? Take care when buying software in auctions. Check out the seller's background before bidding.
Original Equipment Manufacturer (OEM) software refers to full-version software that comes with no fancy packaging or manuals (like we really read the manuals). OEM software usually ships with hardware such as a new computer. These tend to sell for less because of the lack of packaging and a manual.
Furthermore, Microsoft OEM software doesn't include tech support on OEM products. It is legal to purchase OEM products. Pick the suite that meets your needs, search for it on the many shopping comparison sites and research the seller. These steps will ensure you buy a legal copy of Microsoft Office 2007 for the right price.