In this work, the impact of hop constraints on the CAPEX of multi-layer IP/ MPLS over WSON networks is evaluated under different scenarios. By routing lightpaths with different number of transparent hops, the cost of networks varies significantly. This effect is thoroughly analyzed with a heuristic algorithm for different network topologies belonging to some European network operators. The main conclusion extracted is that limiting the transparent reach in such multi-layer networks can give a good tradeoff between CAPEX of IP/MPLS networks and WSON networks, and even lead to significant savings in CAPEX when compared to longer lightpaths routing strategies.