Thanks for the info.
So are these 'fixed charges' at the border of LD150 for a car and LD75, only imposed when a tourist buys the local temporary vehicle importation permit ('TVIP', costing €/$50 for cars or €/$30 for moto)?
In other words, if a tourist has a proper FIM carnet (which in UK from RAC is £185 minimum for the document, plus all the rest), they do not pay the fixed LD charges, but if they buy the local permit for a car - €/$50 (£32) - they also pay LY150 (£75).
Total car cost with TVIP just over £100 (or 100 euros, as stated) versus £185+ with RAC.
If only visiting Libya (as opposed to continuing trans Af), buying local TVIP seems cheaper. Not counting all the other Libyan border costs, of course.