Upvote:1
The Supratours website quotes 120 MAD to get from Rabat, be it Ville or Agdal, to Marrakech by direct train, for a journey of approximately 5 hours:
The quote is also confirmed by the OCNF website (select departure and arrival stations to get a quote):
Moreover, there seem to be no bus service between Rabat and Marrakech (since these two cities are linked by train):
IMHO you are unlikely to find a definitive valid quote online for a grand taxi service from Rabat to Marrakech. This is ever more true since taxi fares are often subject to (strong) haggling. Nevertheless I found a website quoting 192 EUR for three passengers:
All the quoted prices are valid as of the 22nd of December 2015.
Upvote:2
Edit (after the origin city was updated by OP):
Train fares can be found on the ONCF website, but can't be linked to. On this page, there's a "Prix & Reservation" in the left column, where you can search for fares. Rabat to Marrakech is 120 Dirham.
Original:
That sounds rather low. Could it be the price per person, as opposed to the price per taxi? A train from Fez go Marrakech on ONCF costs 195 per person.