Prices are pretty varied, depending on buyers I suppose but also sellers and their knowledge.
I've seen and bought a couple as low as 25m but have turned around and sold them for 195 and 250. Honestly I think 250 is in a topline price for most serverbirths these days, or atleast the common ones, some can go much higher such as leafed mandrakes, laid ginsengs. I know this doesn't really give MUCH help, but these were also prices that I didn't set either, they were prices that I was straight out offered and accepted, both of which were people who were very wealthy so... I wouldn't outright go asking people to spend such gold, but maybe set a fair market value at around 150 and see what happens from there.