Yeah redundancy is going to be expensive. Was your $7k+4k per server or was that for a pair?
It wouldn't hurt to use AWS as a backup though - if you're unexpectedly offline for 24 hours just fire up a big server that is affordable for a short burst.
Each Dell Peoweredge c6100 is around USD$ 1500 -- each server contains 4 nodes . Each node is a dual CPU server with its own RAID ,network port and IPMI port.I think only the power supply is shared with all 4 nodes. have 2 or 3 of these kind of gives a lot of redundancy. The CPU is kinda dated and slow though.
It wouldn't hurt to use AWS as a backup though - if you're unexpectedly offline for 24 hours just fire up a big server that is affordable for a short burst.