As a rough guide, you'll be able to get a three-course meal with drinks in Madrid for:
Inexpensive Under €12 a head
Moderate €12-24 a head
Expensive €24 and upwards
But bear in mind that the lunchtime menú del día often allows you to eat for much less than the price category might lead you to expect; check the listings for details. Most - but by no means all - of the restaurants listed as "moderate" or "expensive" will accept credit/charge cards ( tarjetas ). If in doubt, phone ahead to check.