Best place for comparing a wide range of camera equipment prices is Camera Price Buster, they don't list what type of 50mm lense though (viz all the AF[/D] stuff) and best is only £0.05 more than microglobe (which is FA).
camerapricebuster only lists current new stock, there is only one AF model of a 50mm f/1.8 in production, thats the D version. If you see a used non-D cheap then get it cos the D-feature makes fuck-all difference.
Actually to clarify on models, there are the following:
AF 50mm f/1.8 - first model from the 80s, hard plastic ridged focussing ring, DOF scale behind a plastic window.
AF-N 50mm f/1.8 (sometimes just listed at AF without the N, confusingly) - rubber rocussing ring, better, painted on DOF scale. Same optics at before.
AF-D 50mm f/1.8 - identical to above but with the D feature.