It's roughly $90/mo for 1m+ pvs/mo (includes management). With wp-super-cache you're still hitting PHP/MySQL (although not as heavily if you're pulling everything cold).
Whereas with Varnish you're getting hot pages off RAM and on you go.
Whereas with Varnish you're getting hot pages off RAM and on you go.
Or, you can start with this to get the general idea first: