The best replacement for 50mm 1.8 is 1.4.

The best alternatives to 50mm 1.8 are rated as following:
★★★★★  1.4
★★★★★  35mm 1.8
★★★  40mm 2.8
★★★  85mm 1.8 canon
★★★  kit lens
★★  85mm 1.8
★★  40mm
★  40mm 2.8 canon
★  24-70mm 2.8
★  35mm 2.0
★  85mm 1.4
★  40mm 2.8 nikon
★  40mm pancake
★  60mm 2.8
  50mm 1.4
  canon 50mm 1.4
  35mm
  nikon 50mm 1.4
  50mm macro
  canon 50mm 1.8

Your alternative for 50mm 1.8 is not listed? Suggest!
Speaking about 50mm 1.8, one probably shouldn't forget about extension tube.

Other search terms related to 50mm 1.8 and their ratings are:
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★★★ 5d mark ii
★★ d90
★★ extension tubes
★★ 5d
★★ 60d
★ t3i
★ follow focus
★ t2i
★ 7d
d40
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50mm 1.8
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