Here is where I got the $500 figure. It includes iron but sans tubes. They charge around $125 or the PT.OT,Choke.
http://www.triodeelectronics.com/100wmarshkitv2.html
I have seen some other transformer sets in the $250 range. This is the most I would spend on Iron.
4 12ax7's and 4 EL34 price out around $100 shipped.
Ceritone sells complete wired boards for $100 shipped.
Figure on another $100 in Capacitors from ARS, F&T or Sprague
Lets call it another $100 for chassis,pots, wire, & switches
I don't plan to pay the extra $300 or so in a head shell and face plates. Sourcing parts from Mouser or Allied Electronics should be cheaper too.
Also its much cheaper using Hi-Fi,Fender style or project transformers vs the "Plexi" ones. They jack up the price for that.
on Resale value. The point of building these amps is so I don't have to throw the baby out with the bath water. If there is something about the circuit not "doing it for me" I change it up. Versus chasing tone in the Classified section I will chase tone from my home.
Cool thing is when you buy in bulk you save tons. A $150 transformer can go down to $60 if your buying 10 or more. This is where it would be cool to have a RigTalk group buy in with a manufacturer if anyone was so inclined.