G DATA AntiVirenKit2007 29,95€
avast! 4 Professional 35,95€
G Data includes Kaspersky and avast engine.
Why should I buy avast?
An antivirus is not just the engine (though it’s an important part, of course); antivirus contains various scanners, resident shields, updater…
The engine is only a small part of the avast pro functionality. I don’t believe you get the full avast 4 Pro included with G Data, Web shield, Network Shield, P2P shield, Standard Shield, Internet Messinging Provider, etc. not to mention the increased flexibility of the Enhanced User Interface. Which is confirmed by Igor in his post.
Whilst I don’t know the feature list for G Data the detection engine just deals with one aspect.
I also don’t know where you are getting your prices from but the ones I see are http://www.gdata.de/gdc/gb_start EUR 49,95 for AntiVirusKit 2006 retail.
Avast! 4 Home 0€ ;D
Probably, from G DATA Software homepage. However, Amazon.de has a better price - err…actually, a good price for the packaged version (Edit).
As for the functions, according to this, it has real-time protection to POP3/IMAP, HTTP and instant messaging. Although it doesn’t seem to have P2P protection, it has spyware, rootkits, hostsfile and registry scans. However, probably the feature they seem to be most proud of is Outbreak Shield, which is even able to block “infected mail in 0.5 to 2 minutes after virus outbreak.” According to the description, the application of the latest virus definition is “many hours quicker” than that of rival anti-virus apps… If all of these are true, I think it can be quite a good competitor. Good luck, igor and other team members.
I cannot read German but many words are English. 
I saw your first link but the ‘Trade’ bit in the URL made me think this wasn’t ‘Retail’ price.
Well, at least they doesn’t seem to have English version. 