Hi Doctor
First of all, welcome to the FingerFans community. You've come to the right place for sure, since FingerWorks (FW) is basically history.
I would advise you to keep an eye on eBay to find a TouchStream (TS). You should be able to pick one up for $500-700, but of course with bidding you never know in advance. Yes, that's more than the old retail price but that's a moot point since it's not available in retail anymore. It's a pressed market now and sadly the prices reflect this.
Building a TS from scratch would be a way-cool but immense project. Remember, the FW dudes spent years on getting from scratch to what they had in the end.
Figuring out how to decode the surface and turning it into a USB signal that your OS recognizes as keyboard/mouse devices -- that's probably the easy part. And making the software to tune and customize the device.
Making the sensor array itself is a different matter entirely. It's not simply a touch-screen overlay because such overlays can only handle one touch at a time -- just like a trackpad surface on any laptop computer. The FW sensor array can detect many touches at once, and that's what makes the FW technology so fundamentally different from other touch surfaces.
I don't want to discourage you in your first post, but building this as a home project doesn't sound very likely to succeed. If you measure up your costs in terms of time and materials, you'd probably be better off to spend the money on eBay after all. -- Or wait and see what the next spin of the globe reveals. We still don't know who bought FW, but speculations go in the direction that if it's Apple or similar, then we should start seeing some pretty cool (we hope) devices some time soon (six months to two years from now).