NEW matched pair of 6550/MT88 tubes are $127 on ebay.
NEW 12AX7a on ebay $12 to $20 each. 4 tubes $44 on ebay.
NEW 12AT7a on ebay $13 to $17 each. 2 tubes $26
Total for tubes = $197.
Audio transformers for 6550 push pull tubes are selling for $75 to $90 some priced as high as $150. It will sell for $75 on ebay.
Power transformer for 120 watt push pull power range are selling for$100 on ebay.
The chassie with reverb, 12 controls, knobs, parts, etc is probably the easiest thing to sell $100 on ebay. I just sold 3 old tube amp chassies on ebay I salvaged from old record players for $35, $24 and $56 without the tubes. I think some people already have tubes, all they need is the amp chassie.
Total so far $127, $44, $26, $75, $100, $100. = $472 on ebay and buyer pays postage. Ebay and paypal get about 10% each so that leaves me with $377.
If it is worth $377 as parts then it is worth $377 as an amplifier too.
I priced it for $500 because everyone wants to jew down the seller. I figured someone would make an offer of $250 and we would end up meeting in the middle for about $375.
In 1973 Dynaco 120 amp kits were $45 dollars, now the amps sell for $900 on ebay. Lots of people want tube amps they claim they sound better than solid state amps.