What part of DR is expensive?
Simple answer: Data recovery.
Detailed answer: It would depend on your RPO expectations and data storage/retrieval strategy. If the data is mirrored (in real-time or almost real-time using NAS/SAN), it turns out to be expensive but RPO can be low. However, if the data is stored on tapes, it would be cheaper however, RPO would be high.
Companies like NetApp are a key element for the first approach (Data mirroring approach) while Companies like SunGard are key players for the second approach.