Given all the other options out there, primarily the Holley, I wouldn't pay more than $1,000 for ANY BS3 system.
Upgrades are costly, the boxes are too specific to particular engine platforms, and the resale value is in the tank. Functional, but archaic Atari like software.
I've had both, and would pay twice the price for a Holley than a Big Stuff. The self learning feature also helps get the tune in shape quickly!
If your tuner ONLY works with Big Stuff, that's one thing, but if you tune yourself or the tuner knows Holley systems, keep shopping.
Good luck with it.
Jim