Tonearms - SME 3012, Jelco, or Schick?

I would have a look at the Groovemaster. The best 3012, the 3012r, will be above your price range. I was not impressed with the Jelco 750L, but there was an 850, in your price range, on USAM a few days ago, may still be there. The Schick is also a good sounding arm.

Will your primary cartridge be an SPU, as this would be a determinant of the recommendation?

Audiomods has released a 12" version of the Series Six that is excellent also. There are additional refinements to the design other than adding 2 or 3 inches of arm tube. I acquired one and it is my second favorite arm. 

Ortofon also