Okay, I pulled the trigger on a Marantz 1040 Integrated Amp on ebay for $125. The guy seems to be a top notch seller, and previous vintage receiver sales by this guy (eg Pioneer SX-1250 for $$$) had excellent responses in the feedback. Unlike most sellers, he described the sound, the channel balance, and the cleanliness of the pots. Shipping was relatively low. Given the generally good condition and Marantz name, I can resell it if i don't like the sound. When it arrives, I will compare it to the Bellari HA540 hybrid with the MD 3.0, the HE-400 and hopefully the MD Universal will have arrived by then too.
I expect that it was this low simply because it is "only 20 watts RMS per channel". Of course, for headphones, that will be plenty.
In fact, I would suggest looking for other low power vintage amp & receiver models that are undesirable because most people want to use them with speakers.
In my searches, most vintage items under $100 have a flaw ("untested" or "buzz in one channel" etc) and most of the mid-70s Marantz and Sansui in good shape go for $250 or more.
(I didn't opt for Pioneer amps only because I actually had them back then, and wanted an opportunity to try something else...)
Edited by kstuart - 8/3/13 at 12:34pm