My advice would be to not buy a rotax kart that old. first the chassis even if in good shape will just not be terribly competitve in a tag class. you will need to upgrade the bumper for about $180. the engine is a huge can of worms. you will need a rebuild. The cylinder head that you see outside is merely a cover for the water jacket and will run around $80 for a new one. Typically the crack is in the cylinder so my bet is it is likely cracked also. Then to race it will need to be upgraded based on the age of the kart here is what I would assume would need upgrading to race
cylinder $675 (or more)
clutch and balance gear set $475
airbox $90
evo upgrade kit $1400
the engine rebuild will cost:
$500 labor (at least)
$150 for the complete piston kit
$375 for the rod kit
$75 for the seal and gasket kit
$100 for bearings
you can buy a decent rotax that is current for about $2000
look to buy a chassis that is no more than 4 years old. Older is ok if it is in good shape and there is no intention of racing it. If you want something cheap to get started in racing get a Briggs LO206 kart. with those you can buy an older chassis that is in good condition and be competitive but expect to put a bumper on the back and go through the brake system.