This is best changed on arrival at the airport, otherwise at a bank in Tripoli. Once in the desert there is little to buy except for souvenirs. About 100 Dinar is generally enough for a few drinks some simple souvenirs plus tips for the tour staff. The latter is about 30 to 40 Dinar per staff member. Some monuments charge for taking videos or photos, we pay entrance fees but do not cover any photography fees.
In 2005 100 Dinar is about 40 GBP, or 80 us dollars.