It's relatively easy to build a laptop. You can check out several sites. Tom's Hardware has a video that you can download. You won't save much, if anything, but there isn't much to it. You buy a "barebones" laptop, add memory, hard drive, optical drive, wireless card, and operating system. Barebones can be had from ASUS or several other companies.
I enjoyed Steamed Turtle's sense of humor, and the video at Tom's was fun, too. You'll notice that Tom's builds from the bottom, while Turtle's builds from the top.Tom's tutorialSteamed Turtle's tutorial