1992, Mean Real Gross Income in Euros:
West Germany: 26,408
East Germany: 15,928

Source: 20 Years of German Unification: Evidence on Income Convergence and Heterogeneity by Tilman Brück & Heiko Peters

Meanwhile, income inequality across Germany as a whole actually decreased after reunification because of Easterners getting richer:

While income inequality in West Germany has generally not altered in an economically relevant way over the period 1985 to 1996, inequality in East Germany has increased after reunification. Despite this increase, inequality remains substantially higher in the western part of the country. Convergence of eastern mean income to the western level generally overcompensated the rise in inequality in East Germany, so that the level of inequality in unified Germany is lower in 1996 than in 1990.

Source: INCOME INEQUALITY IN GERMANY DURING THE 1980s AND 1990s – Martin Biewen, University of Heidelberg