Estimating Software Development Costs?

Stu Lalison asks: "I'm an MBA student (but I'm not evil, I promise!) and am working on a business plan that involves having some custom software written for a handheld computer. I've done some research into estimating the costs involved in software production, but when estimating the time involved in writing the software, it usually says 'judge on past projects.' I'm not a programmer, so I don't have any past projects to judge on. I'm wondering if the Slashdot community can give me some ballpark figures on how long it takes a professional programmer to code different parts of a program. I've identified 3 needs of my application: a front-end user interface, a database w/ search function (of about 10 megabytes of data), and integration of both of these into a (currently existing) commercial mapping application. It seems like these aren't huge tasks, but getting (even a rough) handle on their actual complexity will help me greatly. Also, how much development time would be required to port an application like this from, say, a Palm OS device to a 3G handset? Thanks in advance!"