Agreed. There are a huge number of dual stage regs, some new, that you can buy with $100. I don't know why you're looking for only a Matheson ...many models are quite nice, but they're only a fraction of what's available to you at a similar price and quality.
Concoa 212's and Victor VTS250's are my regs of choice. I also recently fell in love with GO regs, and I've taken a liking to Betta's Parker IR6000's.
Where do you guys see a Matheson 3810 series for 100? I would pick it up right away, 100 without a post body kit sound good.