Leonardo da Vinci was a great sketcher, but he's best known for the Mona Lisa. He worked on it four years.
I personally think that there are two ways to go about saving money. The first is to use a photographer that shoots royalty-free images (as I do). That way you'll be able to build your own corporate stock library. Images that will be connected by the thread of your photographer's personal style. You'll find you can use many of them for years, re-using and re-purposing them for brochures, web, trade shows, and perhaps even office decor. Because they're shot by the same photographer, they'll have a "look" that ties them together.
The second thing to consider is this: Do you really need as many images as you think you do? Think about what images you need in order to show that you're different, that show unique capabilities, that can be used in your branding, that will help your image, that humanize your company, that can build trust and desire or communicate quality. Think benefits, benefits, benefits. Your customers don't care about you - they care about what you can do for them.
You're better off with a smaller number of high quality images than lots of images that aren't as compelling.