How much is and old 20000 Turkish lira worth in USD?

About 10 cents.

There are 1,000,000 old lira in 1 New Turkish lira, so your old lira have little money value, just curiOSity value.

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.