Need to share files with others not on site

I have a client on a local domain running Server 2008 R2 (and this server holds all of their files).

What is the easiest, yet safe, way to share a folder of files with other people not on the domain and not on site.  In particular, this company's board of directors (not on site) wants access to certain docs, but of course we want to restrict their access to other folders on the server.

They only need to access documents a few times a year (like meeting minutes, budgets, etc.) and so I'd like a very simple and inexpensive solution.

Any ideas greatly appreciated.

Thanks.
Dave