I’m a bit confused - you said that having them all in a single job takes too much time, and so you want to prioritise the big_job over the rest, but in your original message you asked for them to run in series. Splitting it out won’t reduce the total time to run if you’re only going to start job 2 after job 1 is complete anyway.
How many threads do you have in your job definition? You said AWS spend so I assume you’re using Redshift. Too many threads in Redshift can lead to resource contention and the job actually running slower. I would aim for 4 (maybe try with up to 8 and see where you get a decreasing return).
You might be able to create a single job that contains several steps, something like this:
dbt build -s +big_job --exclude big_job --threads 4
dbt build -s big_job --threads 1
dbt build -s big_job+ --exclude big_job --threads 4
The one thing to keep in mind here is that any nodes that aren’t related to big_job won’t be built using this selector. If that’s a problem, you might be able to express it with a YAML selector but I haven’t spent enough time using those to have any useful guidance.