For Germany: Given minimum wage and tariff treaties the maximum difference is in the region of 5-10% for general duties that you can shift to contract workers - with a disproportional drop in quality. That quality drop doesn't seem to be a problem for those doing the outsourcing though.It's cheaper? At least in Germany we do get away with paying civilian kitchen personal much less than basic grunts.
If you hire directly a civilian cook in the Bundeswehr is ranked equivalent to a StUffz (OR-5) by pay, which no, a simple general cook, butcher or baker wouldn't be ranked at as a soldier.
Contracting in this regard was originally used aplenty in deployment theaters though since you'd have to spend deployment pay on a grunt (... tripling his salary). In recent years this has shifted over to professional military cooks being deployed with contract employees as assistants due to massive quality problems leading to e.g. 200 cases of food poisoning in Masar-i-Sharif.