The Golf Rally was not a 'racing' or 'high performance' version of any kind, in case you are wondering!
It was just a limited edition special trim model of the normal Mk4 Golf. It was released in celebration of the Golf winning the Australian F2 Rally Championship in 1999. The Golf Rally came with 15” Amaroo alloy wheels, slightly dark taillights, and special badges. Otherwise they were identical to the normal Golf Mk4. There were two levels available - the GL Rally (1.6-litre) and the GLE Rally (2.0-litre).
112,000 km is a fairly lowish sort of mileage for a 10-year old car. I had a quick look at
http://www.carsguide.com.au/ and most 2000-model Golfs seem to be going from around $8k to $12k at the moment. There are actually 4 Golf Rallys listed on there right now; 3 GLs from $7496 to $11,999, and one GLE for $11,990. So $6400 sounds like quite a bargain - assuming the car isn't damaged and has nothing wrong with it, etc etc.
If it's in good nick, it would be a very nice 'collector's edition' to have.