Really depends, mostly linked directly to the venue you are getting married. As you can surely appreciate pricing would differ between having a reception at a pub, a boat, hotel or a fancy venue. Using external caterers (approved by venue) could work out cheaper per meal, but you have to consider that you will need to pay additional fees for using the venue's porcelain and cutlery for example.
Meal options would generally be either a formal 3-course sit-down meal with dessert/coffee, or a (finger) buffet. As a rule the latter should work out cheaper with more food per person and more flexibility.
My fiancee and I have arranged for a buffet of finger foods which comes to about £32 per person. A 3 course set meal worked out to £38 per person.
Getting married in a week in Old Royal Navy College in Greenwich.