If you've never seen them before, use the search here for 'overnight' for some thoughts on it, but in short it's quite possible that they are attempting to dazzle you with the cash, either as a TW or to get you to agree to a booking that your brain would say 'nooo' to.
Sub services tend not to be cheap, partly for supply and demand reasons, partly because of the added risk factors. What you charge is, as ever, up to you, but if you can only get this for ?70 an hour or less, is it worth it?