Buying vintage is a good option. I recently found a Yamaha CA-810 integrated amplifier (ca. 1978-79) in excellent condition for only $125 at a used shop here in Seattle. Great sound, tone controls, phono sections for moving magnet and moving coil! And the MM section even has variable loading! Add a nice USB DAC and you're in business for streaming digital music. The incandescent meter lights burned out long ago, so I am replacing them with some snazzy new blue LEDs for just $20. One of these days, when I feel like a little project, I'll see about replacing some of the old electrolytics, which are also relatively inexpensive at any electronics supply.
You'd be surprised at how good the amps were from that era compared to some of the modern stuff. Vintage is a great way to get great sound and save money. It is worthwhile to have the unit checked out by a competent technician before you hook it up to your Harbeths, though!