Hi David:
From what you're describing (mono WAV, etc), this is spoken-word content? If so, I can't see the need for heaping hundreds of dollars on a vintage Nak Dragon. Tascam still makes very good cassette decks, for a few hundred dollars at most. I believe Yamaha also makes cassette decks for the consumer market, and perhaps others, which probably cost less. Any of these will be just fine for spoken word transferred in mono. I'm guessing most of these tapes were made with mono portable recorders anyway?
If I were in your shoes -- assuming my guesses about the audio quality of the content are correct -- I'd buy a moderately priced machine and keep at what you're doing and use the rest of your budget for the pizza and beer party you well deserve for taking on that most tedious task!
If, on the other hand, you were transferring soundboard tapes from a great jazz festival or nightclub, I'd say get a Dragon and shoot for the moon with quality. But I can't see it for mono spoken word tapes.
-- Tom Fine