setup of 5 figures as 2x3 table with 6th cell having the caption

This should get you started. As mentioned by jubobs, since you don't need captions for individual figures, you don't need subfig (or subcaption)

Using tabular:

\documentclass{article}
\usepackage{graphicx,array}

\begin{document}
\begin{figure}[htb]
\centering
\begin{tabular}{cc}
  \includegraphics[width=.4\textwidth]{example-image-a}
  &
  \includegraphics[width=.4\textwidth]{example-image-a}\\
  \includegraphics[width=.4\textwidth]{example-image-a}
  &
  \includegraphics[width=.4\textwidth]{example-image-a}\\
  \includegraphics[width=.4\textwidth]{example-image-a}
  &\multicolumn{1}{b{.4\linewidth}}{\caption{Caption text coming here at the last position}}
\end{tabular}
\end{figure}

\end{document}

Using minipages:

\documentclass{article}
\usepackage{graphicx}

\begin{document}
\begin{figure}[htb]
\begin{minipage}{.5\textwidth}
  \includegraphics[width=.9\textwidth]{example-image-a}
\end{minipage}%
\hfill
\begin{minipage}{.5\textwidth}
  \includegraphics[width=.9\textwidth]{example-image-a}
\end{minipage}
\begin{minipage}{.5\textwidth}
  \includegraphics[width=.9\textwidth]{example-image-a}
\end{minipage}%
\hfill
\begin{minipage}{.5\textwidth}
  \includegraphics[width=.9\textwidth]{example-image-a}
\end{minipage}
\begin{minipage}{.5\textwidth}
  \includegraphics[width=.9\textwidth]{example-image-a}
\end{minipage}%
\hfill
\begin{minipage}{.5\textwidth}
  \caption{Caption text coming here at the last position}
\end{minipage}%

\end{figure}

\end{document}