\subsection{Elements of costing}
One of the aims of the design study is to produce a detailed costing of the TLEP project. Not surprisingly, the main cost drivers for the whole complex are expected to be the tunnel, the shafts and the related services and infrastructure (including access roads). The TLEP project, however, may be considered as a precursor to the VHE-LHC, in which case the corresponding cost would be shared between TLEP and the VHE-LHC. The length of the tunnel will be optimized on the basis of geological and accessibility criteria. For example, a tunnel of 100 km (also shown in Fig.~\ref{fig:TLEP80}, and for which a feasibility assessment is ongoing) might be more cost-effective than the 80~km version~\cite{OsbornePrivate}. 

Besides, the cost of the accelerator and collider rings, dominated by the 600-m-long RF system and the 80~km of low-field magnets -- possibly recyclable for the VHE-LHC injector -- was found in a very prelimimary estimate to be smaller than the LHC cost (Table~\ref{tab:cost}). In view of the large number of Higgs bosons, Z and W bosons, and top quarks to be analysed in very clean experimental conditions, TLEP is therefore expected to be exceedingly competitive. 

\begin{table}
\begin{center}
\caption{Indicative costs for the main cost drivers of the TLEP collider.\label{tab:cost}}
\begin{tabular}{|r|r|}
\hline Item                          & Cost (Million CHF) \\ \hline 
%\hline Bare tunnel and access shafts            &   3,100 \\
%\hline Tunnel services and additional infrastructure & 1,000 \\
\hline RF system & 900 \\
\hline Cryogenics system & 200 \\
\hline Vacuum system & 500 \\
\hline Magnets systems for the two rings & 800 \\
\hline Pre-injector complex & 500 \\ \hline 
%{\bf Total} & {\bf 7.0} \\ \hline
{\bf Total} & {\bf 2,900} \\ \hline
\end{tabular}
\end{center}
\end{table}

%The length of the tunnel will be optimized on the basis of geological and accessibility criteria. For example, a tunnel of 100 km (shown in Fig.~\ref{fig:TLEP80}) might be more cost-effective than the 80-km version. Indeed, a 100-km tunnel may avoid the limestone areas in the vicinity of the Sal\`eve mountain (more difficult to dig), and might not require digging either challenging 1-km-deep shafts or a 30-km bypass tunnel needed to access the caverns underneath the Sal\`eve mountain (as shown in Fig.~\ref{fig:Profile80}, taken from Ref.~\cite{cite:Osborne}). With such a tunnel, the physics case would be enhanced with a 20\% larger luminosity at all centre-of-mass energies, and it would be possible to increase the maximum centre-of-mass energy by 5\% with the same RF voltage, should there be an interest to do so. A feasibility assessment for the 100-km version of the TLEP tunnel is ongoing.