The price sounds a bit high, but it's more likely to be along the lines of
1) create new icons, including resizing them and editing into appropriate dimensions, colour depth etc
2) Handle easy cases of new images in new location, then harder ones of 'image embedded inside something else'
3) Manually go through each page, with a search to help speed task. Automatic cut and paste is a recipe for disaster and does not always preserve grammar.
4) Fix code which accidentally had a hidden dependency on company name being the previous one
5) Document everything, in case customer comes back two weeks later and complains about what has been done, the cost, time etc.
6) Test internally
7) Implement on test site, for customer to test thoroughly.
8) Swap live with test in early hours
9) Fix bugs after it's found the customer didn't state their requirements correctly, or test the test site, even though they signed it off.
10) bill large amount, say 700 quid+ per day.
It might be a five minute job, but I bet they haven't arranged the system so it is.