dwalin,
Cheap in one sense, since hey what's $10K in a $100K project right?
But if you look at the actual figures...the redundancy offered by the S87xx solutions cost 3X of a simplex, S8500 solution. And at the end of the day, both run comunication manager and will provide dial tone to your phones...
That said, I would STILL go with the S87xx solution over the S8500 if I had my choice.
Aside from the reliability & redundancy of the two server solution, having both servers also allows you to perform more work outside of your "production" environment. If you need to install a service pack, do it on the backup server first....if something goes wrong, no harm no foul.