We did a quick survey of the competition (Dec 2010). From what we found on the web these are approximate prices in USD (any corrections are welome),
Forensics ToolKit (FTK), $4,330
EnCase Forensics, $ 3,000
ProDiscovery Forensics, $ 1,495
X-ways Forensics, $1150 (779 Euro)
Helix 3 Pro, $ 239 (discontinued it seems??)
P2 Command Kit, $1,995
OSForensics Pro, $799
OSForensics Free, $0
PLUS, this doesn't include ongoing support costs, which can double the initial purchase price over 5 years.