How much is 500000 old Turkish lira worth if you can get it exchanged?

Yes, about 42 cents US. There are 1,000,000 old lira in 1 New Turkish lira, so your old lira have little money value, just curiOSity value. (1 New Turkish lira is worth (March 2009) about US$0.75.)

Any remaining old lira has to be converted at either the Turkish Central Bank or T.C. Ziraat Bank branches, at the rate of 1 million old lira = 1 new lira.