Market is pretty thin making price discovery difficult. To put it into a tiny bit of context, there are something like 30 or so Ferrari 250 GTOs. Prices seem to vary from $14 M to $50 M (somebody really, really wanted a GTO).
Check the forum. Seems to me a Zanardi recently went for some where around $140 k. If it is in the right condition and you can find the right buyer who really wants a Zanardi, then .....