Hey @janriemer, thanks a lot for this input/feedback/thoughts.
I think the --dry-run arg should be the answer to what you suggest, which eventually should show you the potential cost of it, if it is effectively possible to estimate the cost.
Some other thoughts were that the interactive shell we envisioned to have, can perhaps be the place where it prompts you for many things including the potential cost perhaps, so you could then jump into the interactive shell with just running safe, and then inside of it you are prompted for several things and defaults are inverted, so e.g. in interactive shell you do:
$ safe
Welcome to SAFE CLI interactive shell!
Type "help" for more information about supported commands.
Type "exit" to exit this shell. Enjoy it!
safe >> files sync ./localfolder safe://mysite
Files will be uploaded recursively, is it ok? [Y/n]:
We will be updating 'mysite' NRS name as well, is it ok? [Y/n]:
This operation will cost ~ 0.000044523, is it ok to proceed? [y/N]:
...
Having those configs about expenditure could be also possible and a nice idea, perhaps that could be stored locally in a config file, or even within your SAFE account and the CLI reads if you are logged in.
Just in case you didn’t know, you can already try it out, and we’ve been using a shared vault also, so it’s not in the wild wild, but a bit wild 
, if you weren’t aware look at this: New Release: Vault Phase 1 (real vault), the User Guide is up to date with latest version available (v0.3.0) and it’s here: https://github.com/maidsafe/safe-cli/blob/master/README.md