It takes about 4 hours to upgrade. And since it's broken, add an hour for repair. So that's 5 hours. So let's say it breaks weekly (he's unlucky if I remember correctly, and he writes like a madman) that is §50 and half an hour every week. So after 10 weeks you could possibly have one less book written, worth, let's say, §250 x 6 weeks' royalties (so you lose §1250) which equals at most 3 weeks' replacement cost. To find the balance we equal the time. So it works out at least 3,33 times more expensive to replace.