secure mail

We are looking into secure email solutions for sending sensitive/restricted information via email to external recipients. Our email platform is exchange 2010 and on the computers outlook 2010. What I don't understand is if one of our internal employees wants to send email to an external recipient in another organisation via whichever secure mail solution we decide on, do they (the recipient) also need to invest in some compatible secure email software, or not really? Please keep answers low tech management friendly. I cant see that going down well with recipients ("we can only send you secure email if you invest in a $$$ software package from your side also").

There also seems to be many solutions for secure email ranging from free products to quite expensive products? Are there more expensive solutions " more secure", or if not why they difference in price? If it is because they are more secure, can you elaborate what exactly is more secure, and the risks associated with the free/cheap options? I cant understand why anyone would pay for a solution if there is a free alternative, so please enlighten me (again in management friendly low tech terms) why the paid options are often more desired.

\if you wish to recommend some products and pros and cons on the various options then that would be great...