I have a 96 SL600 and everything is expensive on the car. The 93 was a sole year of production for this type of 600sl. That means there are parts found on the 93 not found on any other sl which translates into higher costs. And that is if the parts are available, check fastlane, some parts for this car are not carried so your only resource will be the dealer. By 90k miles, the shocks are probably shot which will cost you $2000 to repair. Plus you need new o2 sensors and mass airflow sensors to keep everything in check. Plus a complete tuneup changing all the fluids on the car. If I were you, I would take it to the dealer and have them to check every single component imaginable and very important to have a smog check. I have my sl, smog checked every year, to make sure everything is ok. If it fails or borderline, walk away from the car. Some of these V12s ran rich for a brief moment and their motors were destroyed. Basically, the 600 is an expensive motor, the sl is an expensive car, and it is a sole year production. My advice is to buy a 98+ SL500. I would stay away from the 93 model unless the previous owner worked out everything and the car was meticulous kept after.
P.S. Check the tires for depth. My SL eats tires although I dont have AMG wheels.