Have you ever been inside of one? They are a bit cramped for most adults. The MTLB, on the other hand, is quite roomy inside and tolerably easy to move around in while stooped down. Passage to the cockpit is even easy to maneuver through, far easier than the BMP series.
That being said, I truly don’t know the values, but $50k for an operational OT-90 sounds reasonable to me.
I do sometimes watch Warsaw Pact armor values out of sheer curiosity. I don’t watch the popular auction site often. But I had seen there, in the last ten years or so, a basket case BTR60 sell for about $7k as I recall, a “roller” very nice-looking BTR60 with recent paint but no engine sell for around $13k, and the weathered shell of a BTR50 for about $10k. All located CONUS.