The Titanium is very hard to drill: it wears the tools and, as it is very long to work, it even can catch on fire (hence color the metal too).
Gold on the other hand is much more easy to manipulate and to shape.
However, I don't know where you saw that the prices were close. From what I always new and the prices today, there is a very significant difference in pricing (more than 20% rise for the RM010 for instance). Here is a good link from Andrew about the case production : richardmille.watchprosite.com
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In higher budget RM watches the difference is lower as it doesn't represent much of the total price.
Hope this helps.
Cheers, Mark
PS: The RM027 is made of Carbon nanotubes polymer, not NTPT
This message has been edited by Mark in Paris on 2015-06-01 14:42:06