that depends on how you configure the pipeline.

If you have f.e. 10 jobs and you run those 10 jobs in parallel, then 10 job clusters are created.

So you start paying for 10 clusters.

You could also process them sequentially. Like that you only use 1 cluster at the time. However you have to wait to provision each cluster, which is indeed wasted money. Hence I mentioned the cluster pool (warm nodes).

But you could also create f.e. 2 pipelines with 5 notebooks each, and if you use cluster pools you do not waste money/time waiting for nodes to be provisioned.

Running jobs on interactive clusters is almost never cheaper. Remember that parallelism also means jobs are finished faster.