The risk of giving a stranger - trustworthy as they may be - full access to my user account, far outweighs the cost of a new drive. On the occasion that I've had send my laptop in for repairs, I removed my drive, put in an old one and loaded a fresh OSX on it. If it was a drive that died I would just suck it up and pay for the replacement myself.
I realise this doesn't work with the built-in SSD models though. I haven't been in that situation, but since I do use FileVault2 and dilligently keep backups, I would just tell them to wipe the drive.