Windows – Best way to restrict access to a folder in Dropbox

I currently run a business with around 10 staff members and we currently use Dropbox Pro 100GB to share all of our files.

It works very well and is inexpensive, however, I am taking on a number of new staff and would like to move the more sensitive documents into their own, protected folder. Currently, we all share one Dropbox account, I am aware that Dropbox for teams supports this, but it is far too expensive for us as a small company.

I have researched a number of solutions:

1) Set up a new standard Dropbox account just for use by management, which will contain all of the sensitive documents, and join the shared folder of the rest of my team to access the rest of the documents. As i understand it, this is not possible with a free account, as any dropbox shared folder added to your account will use up your quota

2) Set up some sort of TrueCrypt container, and install TrueCrypt on each trusted staff member's machine, and store the documents inside that.
Would this be difficult to use? I'd imagine the sync-ing would not work so well as the disk would technically be mounted at the time of use and any changes would be a change to the actual container rather than individual files.

I was just wondering if anyone knows a way to do this without the drawbacks outlined above?

Thanks!