Example from the Retina Auto III, with the 50mm F2.8 Xenar. Exposure using the still-good 1964 Selenium Meter.
This camera was $20. It is a non-folding Retina.
One other consideration for you to use Cokin filters- it would be best for the front of the lens NOT to rotate as you focus. The Retina IIIS lenses do not rotate.
BUT: The lenses on the Retina Non-Folding Fixed-Lens cameras rotate as you focus them. That makes the square Cokin filters a pain to use.
I still think your best bet in the Retina RF line for this work is a IIIS.