Hard to say. We're talking a tap, double check valve, other fittings, some copper tube to run the water through and some larger-bore tube to sleeve the tube where it passes through the wall, some filler, mortar, and sealant. Nothing massively expensive. Drill the wall (easier or harder depending on what it's made from), filler or cement the larger tube in place, fit the rest of the pipe work.
Main cost is labour, and I would personally be quoting for two hours, because there is always something that isn't quite simple.
But, given the current Covid-19 circumstances, even if I weren't currently stuck abroad, this isn't something I would take on at this present moment.