Mustufa, lux, candela et al not relevant for practical, uncomplicated photography, just EV scale, aperture, shutter speed, iso adjustment, and maybe (if using flash a lot) split balance/ambient flash. In terms of pricing, a second hand Weston meter could be had for $30, but it would probably benefit from being thoroughly checked out if it is looking quite old. I personally will not buy second hand meters under any circumstance.

The "moon dome" is called an invercone. It distributes/diffuses light evenly onto the very sensitive photocell lurking below. It is used for incident and reflective metering, but not at all for spot metering (for those meters that offer spot metering).

Not sure what you have come across referring to a digital lightmeter for surveying? Or how something that is good and proper for surveying might be just as useful for photography.