DisplaySearch analyst Hiroshi Hayase posted about Samsung Display becoming the world's largest small/medium display maker. In his post, he notes that the average price for a 4.3" qHD (960x540) LCD was under $23, while a similar AMOLED costs over $33. A 4.8" HD AMOLED costs over $50 (a 4.7" HD LCD is only $36).
According to iSuppli, the GS4's 5" Full-HD Super AMOLED display costs $75., and the 4.8" 128-x720 AMOLED on the GS3 costs $65. These estimates include the touch panel though (embedded in the Super AMOLED displays).
Hiroshi Hayase says that AMOLED displays may have a competitive advantage in 7" to 8" tablets due to their low power consumption and high color gamut, and it's likely that AMOLED displays can have a more near-term influence on tablets than on OLED TVs.