Tanzania - Mali trip

We plan our trip from Europe to Tanzania and Mali in Dec/Jan 2003.
Can anyone advise us how to create the cheapest flight schedule from Europe?
As far as I know there are two options.
1) Two separate trips starting in Europe and return Europe.(Frankfurt-Bamako-Frankfurt Frankfurt-Dar es Salaam -Frankfurt)
2) Go to Tanzania or Mali and find the cheap flight from coast to coast.
How much is the flight from Addis Abeba to Bamako(one way / return)?
Also I have read of flight from Marseille to Gao (Mali) by Point Afrique - is it true?

Please advise

Monika