I had a HD freeze on me one time I rest it and about 2 hours later it crashed. Luckily I did a backup and I had a spare. You should be able to pick one up for a very reasonable price but if it crashes and it has to be over-nighted they charge accordingly and so should you. If you've explained it to them and they want to wait it's on them. I've got a few clients like that. Sometimes saving a dime now will cost them a dollar later.