I used the approach (actually it was nearly the whole solution) contributed by @student and revised the code given by @Altermundus to look exactly like the figure in question.
\documentclass[a4paper]{report}
\usepackage{tikz}
\usepackage{verbatim}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage{subfig}
%-------------------------------------------------------------
% Call pattern library and declare DIN conform
% vertical hatchings
%-------------------------------------------------------------
\usetikzlibrary{patterns,calc,intersections,patterns}
\pgfdeclarepatternformonly{dinhatch}{\pgfpointorigin}{\pgfqpoint{1mm}{100pt}}{\pgfqpoint{1mm}{100pt}}% Adjust the second 1mm for your needs
{
\pgfsetlinewidth{0.4pt}
\pgfpathmoveto{\pgfqpoint{0.5pt}{0pt}}
\pgfpathlineto{\pgfqpoint{0.5pt}{100pt}}
\pgfusepath{stroke}
}
%-------------------------------------------------------------
% Call arrow library and declare DIN conform arrowheads
%-------------------------------------------------------------
\usetikzlibrary{arrows}
\makeatletter
\pgfarrowsdeclare{dinarr}{dinarr}
{
\pgfutil@tempdima=0.5pt%
\advance\pgfutil@tempdima by.25\pgflinewidth%
\pgfutil@tempdimb=7.29\pgfutil@tempdima\advance\pgfutil@tempdimb by.5\pgflinewidth%
\pgfarrowsleftextend{+-\pgfutil@tempdimb}
\pgfutil@tempdimb=.5\pgfutil@tempdima\advance\pgfutil@tempdimb by1.6\pgflinewidth%
\pgfarrowsrightextend{+\pgfutil@tempdimb}
}
{
\pgfutil@tempdima=0.5pt%
\advance\pgfutil@tempdima by.25\pgflinewidth%
\pgfsetdash{}{+0pt}
\pgfsetmiterjoin
\pgfpathmoveto{\pgfpointadd{\pgfqpoint{0.5\pgfutil@tempdima}{0pt}}{\pgfqpoint{-3mm}{0.5mm}}}
\pgfpathlineto{\pgfqpoint{0.5\pgfutil@tempdima}{0\pgfutil@tempdima}}
\pgfpathlineto{\pgfpointadd{\pgfqpoint{0.5\pgfutil@tempdima}{0pt}}{\pgfqpoint{-3mm}{-0.5mm}}}
\pgfpathclose
\pgfusepathqfillstroke
}
\pgfarrowsdeclarereversed{dinarr reversed}{dinarr reversed}{dinarr}{dinarr}
\makeatother
%-------------------------------------------------------------
% Begin document
%-------------------------------------------------------------
\begin{document}
\tikzset{add/.style args={#1 and #2}{to path={($(\tikztostart)!-#1!(\tikztotarget)$)--($(\tikztotarget)!-#2!(\tikztostart)$)\tikztonodes}}}
\tikzstyle{LabelStyle}=[above=2pt]
\tikzstyle{state}=[circle,thick,draw=black!75,fill=black!20,minimum size=6mm, text=black]
\tikzset{dot/.style={draw,circle,minimum size=1.4mm,inner sep=0pt,outer sep=0pt,thick,fill}}
\begin{figure}[!htbp]
\begin{center}
\begin{tikzpicture}[font=\footnotesize]
\draw[-dinarr] (0,0)--(9,0) node[below left,align=left]{Umfang des\\ öffentl. Gutes X};
\draw[-dinarr] (0,0)--(0,7) node[below left] {Geld};
\path[pattern=dinhatch,pattern] (3.5,3)--(4.7,1.5)--(4.7,4.9)--(6.2,3)--cycle;
\coordinate[dot,label=below:0](O) at (0,0);
\coordinate[label=left:tp](tp) at (0,3);
\coordinate[dot,label=above right:C](C) at (3.5,3);
\coordinate[dot,label=above right:G](G) at (6.2,3);
\coordinate[label=above left:E](E) at (4.7,3);
\coordinate[label=above right:D](D) at (4.7,1.5);
\coordinate[label=above right:F](F) at (4.7,4.9);
\draw (tp)-- (9,3);
\draw (C) -- (C|-O) node[below] {$\mathrm{X^{A}}$} ;
\draw (G) -- (G|-O) node[below] {$\mathrm{X^{B}}$} ;
\draw (E) -- (E|-O) node[below] {$\mathrm{X^{(A,B)}}$} ;
\draw[add = .8 and 1,line width=.45mm] (D) to (C) node[above] {$\mathrm{MZB^A}$} ;
\draw[add = 1.3 and 1.2,line width=.45mm] (G) to +($(C)-(D)$) coordinate (X) node[above] {$\mathrm{MZB^B}$};
\draw (D)--(F);
\end{tikzpicture}
\textit{Abbildung 26.1: Anpassung des Angebots öffentlicher Güter durch gebietskörperschaftliche Aufgliederung}
\end{center}
\end{figure}
\end{document}
What yields following figure: