I have the Minolta Maxxum AF 50/1.7--you can get one for under $100 and they work great with the Sony cameras.
The older versions of the 50/1.7 have 7 straight blades, which sometimes makes for weird bokeh, but it's a very sharp lens, great colours and lots of pop! I prefer the look though to the Pentax 50/1.7's, which all had 6 blades.
This one was at f/2.8. Not bad for $90!
(They reworked this lens with rounded blades too--that version goes for more, and you can tell it by the rubber manual focus ring and it also says "AF 50" on the side instead of "AF lens.")