I'm in no position to speak for Valentine, just a happy customer, but I've never heard of him offering any group buy discounts. If he did, I'd imagine the quantity would need to be quite a few.
I've used both the V-1 (currently have three) and the Escort 8500K50 (currently have two), and the Valentine is far Superior, in my opinion. They both have excellent range and false rejection, but the POP detection is much better in the V-1. I can't even use POP on my 8500's, as they false way too much if I do. Here in Florida, the HP is rapidly switching to POP, which leaves the 8500 (and my built in K-40's on my cars) almost defenseless.
The V-1 costs more (and it needs the audio interface), but one ticket would cost way more than the difference. I just sent in my third one to them to upgrade today. Mine are almost three years old now, and latest upgrade, including POP mode that I didn't have before was 75.00 USD each plus shipping (previously, turn around was about two weeks, including shipping both ways). As far as I know, the Escort isn't upgradeable. I look at like the more I use them, the cheaper they get!