The sheets almost certainly don't cost that much new. I guess if the hotel rents their linens that might be the charge they incur from their supplier for a "deep clean". Even so, even if there is a cost, I'm quite surprised a hotel has charged you... as you say, stained sheets are just part and parcel of a hotel! You mention you stay at this hotel often, is it with your husband? I wonder if they are not specifically charging you for these sheets, but are trying to discourage you from staying because you are often staining sheets... but even that doesn't make much sense if you are washing the sheets yourself when this happens. Maybe it is a mistake? I'm kind of baffled that a hotel would even try to charge a guest for anything other than egregious and intentional damage.

If they are intentionally trying to charge you, then I agree with the other respondent, I would expect a response outlining your husband's disability to have the charge waived.