It depends. I'll cover Scotland as that's my area of expertise, but in the main it's similar across Western Europe.

There were two forms of service in Scotland. "Free Service" and "Scottish Service". Free service was performed by all free men (i.e. the barons, thanes, knights, serjents and all other freeholders) and would be horsed and have a range of good arms and armour, the numbers depending on the terms of their fee charter. Scottish Service was (primarily) demanded from the earldoms north of the Forth and consisted of all able bodied men and who would fight on foot (and who may or may not have some form of body armour (a jack or other padded leather).

In general the period of (unpaid) service was for 40 days.

A periodic 'wapinschaw' would also occur (issued by the crown) which would require either or both forms of service to assemble for an inspection of arms and equipment.

There was also (largely post Robert I) ship service required of the large fleets maintained by the lords in the Isles and Argyll.

Edward I modified the service aspects of the English feudal armies so that the full host was not called out and then went home after 40 days but rather a portion was called out and served beyond 40 days for wages either paid by the crown under rolling 40 day contracts or at the particular lord's expense (there are numerous extant wage rolls for the Welsh, Scottish and French wars - eg an archer was paid 2d per day for service in Wales). Morris has some excellent coverage of this change in English service post 1277.

Mercenary soldiers became increasingly common from the late thirteenth century (for those who could afford them) and particularly professional (archers, crossbowmen, light scouts - hobelars, and foot).

A list of medieval prices and wages is sourced at http://medieval.ucdavis.edu/120D/Money.html

Sources: GWS Barrow Robert Bruce & The Community of the Realm & Kingdom of the Scots. JE Morris, Welsh Wars of Edward I, M Prestwich, Edward I.