To keep it simple, the most obvious solution would be to add a second OM body. If you find the OM3/4 too expensive, maybe an OM2sp can fit your need. It is pretty similar to an ONM2 with spot metering capability.
The question now is to find one 100% working. I am not sure these cameras age well so it could be a challenge.
Other solutions exist (Nikon, Pentax, you name it) but you lose the compatibility with what you already have.
For $200-300, I am not sure you will find the MF camera you want as such camera would be rather recent and would command a higher price tag.
Take care... and welcome to the forum!