OK, learned something new today!
Here's a list from 1959 that shows the original pricing of the entire US model line:
Note that the gold-top Seamaster Grand Luxe is only $35 (in 1959 dollars) more than the standard gold-top Seamaster. That's likely the cost of the 18K gold dial. However, the Seamaster Grand Luxe with the 18K dial is $55
less than the cheapest gold-top Constellation that didn't have a solid gold dial.
To my knowledge, there were no Seamaster Grand Luxe watches with solid gold cases. But of course, I've been wrong before in this thread.
You do have to remember that the US-only Grand Luxe and the Globemaster at this time were using the obsolete cal. 501/503 movements while the other Seamasters and Constellations had moved on to the cal. 55X/56X series, which were brand new for 1959.
Hope this helps,
gatorcpa