One of the least expensive, but good finders, is the
35/85 combo made in Germany for the Kodak Retinas.
Unfortunately, they don't work on early Leica types...
they're offset to the right - blocks the shutter speed dial.
Work fine on KIEVs and others.
I have several Helios finders, but have a hard time alligning
my eye (glasses) to see the frame clearly.