Sure, but paying $325 for used MK25/S600s in need of servicing, and then having to pay full price for servicing, is on the high end for used regs. A more typical example would be paying somewhere around $200 for a MK20/G250, (or G500) which is quite comparable to the top-of-the-line MK25/S600, or $100-150 for a MK10 (or 15) with the same 2nd stage. IOW, the biggest savings in used comes from buying older model regs that perform just as well. Another big savings comes from not having to service every year just to maintain the warranty, and instead servicing only when the reg needs it. MK25/S600s that are rebuilt really well and taken care of properly should last several seasons before needing to be rebuilt. Of course, I suspect in your case you dive quite a bit more than a typical recreational diver.
You ended up with exactly the reg you wanted, which is good, and I"m sure you don't feel bad about the price.