For the price, why not look into old Ascension or Polhemus systems instead? For example, TheLostBrain is selling a complete setup for $1000 I believe...
Not particularily interested in an old Flock of Birds, it's a bit of overkill for what I want and the sensor cube is huge.
I already have three Polhemus InsideTrak devices, frequency modules and sensors along with a rather old Polhemus FastTrak. The InsideTraks would be ideal but they're all ISA bus devices and I'm not sure how they'd perform on the adapters you can buy.
Also what I have in mind would need to be repeatable (hopefully) so once I'd got past the development stage I'd need to be able to get new devices.