The headliner is a PITA to replace. The trim pieces on the pillar posts are very hard to pull off without breaking the little tabs that hold them on. Also, those trim pieces are covered in a felt flocking that does not like to be handled and are total dirt magnets. Keeping clean hands while working on the headliner is a must.
I was quoted $400 by a shop to do the whole thing.
I had to removed the headliner to replace the sun roof, anyway. So I took the foam core out by myself and took that to the shop and the price lowered to $180.
I am sure it can be done with a DIY kit at home a little cheaper.
As a new P38a owner - your next stop on the INTERWEB needs to be www.rangerovers.net and find the forum on that site. The Range Rover has so much electrickery in it and this site has a reference for almost every way-to-common repairs.
Firemanshort
1980 Stage One
(Past owner of 1973 Series III - Highlander)