\subsection{Elements of Costing: Alternative}

A detailed costing of the TLEP project does not exist yet, and one of the aims of the starting TLEP design study is to produce it. Since the CERN site already exists and needs not be paid for, the tunnel, shafts and related services and infrastructure (including access roads) are expected to account for the largest fraction of the cost of a 80-km version of TLEP. However, the TLEP project may be considered as a precursor to the VHE-LHC, in which case the
tunnel, the tunnel services and the magnets (which could be used for the VHE-LHC injector) could be shared between TLEP and the VHE-LHC. The next two cost drivers of TLEP are the 12 GV RF system and the 80 km of magnets. In addition, the cost of the (up to) four detectors should be added: they are expected to have costs between those of the LEP and LHC detectors. In view of the large number of Higgs bosons produced at TLEP, the cost of each Higgs boson is expected to be exceedingly competitive.

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 not be more expensive than the 80-km version, since a 100-km tunnel may avoid the limestone areas in the vicinity of the Salève mountain that are more difficult to dig, and might not require digging either challenging 1-km-deep shafts or a 30-km bypass tunnel that would be needed to access the caverns underneath the Salève 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.