Ok, I know you specified just a 50mm, but if you have that budget why not consider keeping the Olympus body & adding either the VF2 or VF3, the decent Panasonic 14 2.5, the Panaleica 25 1.4, & the excellent Oly 45 1.8?
As suggested, buy used...Sell the 20...
A decent kit (28, 50, 90) for around 1k.