> is move(n,m) the only operation with a "cost" ?

Practically yes. Finding the right order is easily achieved with Perl in memory. The cost mainly results from time a robot arm needs to pick and move a tape. (about 30 seconds)

I neglect the time difference for tape moves betwenn different slots. (a maximum of 60 tapes)

> Would a solution that analyzed all of the slots in detail first,then built up a list of moves be considered optimal?
Yes - that's how I want to solve it.