Hi Scott - That's not so easy to figure out since I ended up changing the design a few times along the way and ordered parts I didn't end up using (at least for these amps). I'd guess somewhere between $800 and $1000 for each mono amp.
I bought the chassis on ebay from a vendor in China, the transformers with covers from Antek, the connectors from Parts Connexion, the F5 PCBs from DIYAudio Store, the soft start and power supply PCBs from XRKAudio Etsy store, the Jensen transformers (for balanced input) used from an ebay seller, the Copper input caps from SonicCraft, and all the rest of the parts from Mouser. I had the small PCB boards for the balanced input circuit made by a shop in Taiwan.
Building amps like this isn't a way to save money. In addition to all the parts, I also bought a nice soldering station, a Variable AC transformer, a heat gun for heat shrink, two nice Fluke multimeters (I had a cheap one), and a 4-channel oscilloscope. The scope isn't really necessarily, but everything else is. You can get away without the variable AC transformer, but it significantly reduces the risk of blowing parts and/or starting a small fire if you've got a wiring error, and they are not very expensive.
It's definitely possible to build an amp similar to this for a lot less. For example, the standard FirstWatt F5 uses a single chassis, a shared simple power supply, no soft start (other than a single simple thermistor), no balanced input, no copper input cap (which is used to roll-off the low end for use with OB subs), no tube connectors and no thermal shutoffs. I would expect you could build one of these for well under $1K for a two channel amp.