You have my sympathies Slowmo! I know how painful it can be - I've transcribed 70 interviews, but have done this over 18 months so it's been fine. Sounds like you couldn't do them as you went..Build in more rewards I reckon. The holiday's a good start, stick a photo of where you're going on the wall. Bribe yourself with nice tea or chocolate - or something stronger if you need to! Cross off the remaining 23 interviews as you do them. And can you alternate doing this with a more interesting, or at least different task?
You're over half way though, keep going!