Originally Posted by kjpmkjp
Edit- Technics SL 3200:
This Technics has a slightly higher mass tonearm than either the Ortofon or Grado is perfectly suited for so you should also consider a Denon High Output Moving Coil like the DL-110 which should be around the 100USD mark, perhaps slightly more.
This will give you a similarly lush presention to the Grado. If you want something more incisive then the Audio Technica AT440 is another good one to consider as it has a really high quality stylus which is a big leap over most at this price point.
The Denon is probably the best match though. Read about some cartridge comparisons on the SL1200 here
Technics SL-1200 MkII turntable - [English]
and the arm on this is actually lower mass than yours I believe.
Either of these is a big jump over the Stanton 500AL with standard conical stylus. If you don't want to spend this much money then I think there is also an eliptical stylus available for the Stanton which may well be your cheapest upgrade path.