If you're racing beer leagues, get a detuned GS with a cheater sidecut (16m or so): you won't be racing real slaloms, only tight gs courses with a lot of gates. If you're racing masters or real courses, buy two pairs: gs ski in slalom course will be unskiable, slalom ski in GS course will feel dangerous after 4 gates. If you can only buy one pair, get GS skis and get good at that discipline first and then buy slaloms once you have the money. It is the cornerstone of racing, the holy grail, the foundation. No good racer doesn't have mad GS skills, wether he is a speed specialist or a slalom freak.
If you're only looking for a racing ski to have something substantial attached to your feet, something like the Fisher Race or WC RC or SC would do the trick.