For reference, I'm seeing PBK/RBK costs escalate to like 5k-9k even for 23-26 yr olds with low/mid 80s ratings, compared to ~1500-2000+ for PMV/FMV. It's just night & day to develop OL compared to any other position, where my anecdotal feeling has matched up pretty well with your findings. I don't feel any other position needs a boost and 1-2 might even need more like 90% (QB & TE were your choices and this feels solid to me).
I'm an analyst IRL, so I don't want to go by feel, but I do think there's something beneath the "not-terrible-looking" #s for OL. Then again I'm dealing in tiny sample sizes and could easily have just had very bad OL prospects that I've tried to progress thus far. Thanks for your effort so far to try to quantify some of this, it's very helpful.