Tektronix 1720 Vector Scope
The Tektronix 1720 vectorscopes are available for 20-50 on eBay since most TV stations are decomissioning all of their analog NTSC gear. It is a cheaper alternative to the Vectrex for art projects or a compact MAME display, although the beam is not quite as sharp. Shipping is usually much expensive than the price of the scope, since it is typically a 19" rack mount combo with the 1730 waveform monitor.
Games like Tempest and Lunar Lander are totally playable, although the smaller display makes the fonts very tiny. The voltage range in this case is -2.5 to +2.5 volts, which is just about the right vertical, but a bit low for the horizontal. This is using the output of the MPC4922 DAC directly, rather than going through my opamp circuit (which made things fuzzy).
It is a very deep tube due to using Electrostatic deflection (instead of magnetic deflection, like in the Vectrex). This makes it fast, but requires a very long tube to magnify the effect of the small deflection angles. It that would look great in an clear acrylic case, so I might re-house it. I'm not sure what to do with the 1730 at this point.
The manual (PDF) for the vectorscope has a misprint on the XY input port pinout. Pins 7 and 5 are ±X while 3 and 1 are ± Y. You can run the inputs single ended by grounding the minus inputs and swinging the voltage ±5V.
For the Tek 1740A, the port is a DB25 and the pinout is in the manual: