Glad you solved it. Here is my advice otherwise:

They could conceivably try to extend the visa when they are in Saudi. Find a local agent or ask the hotel concierge. This is sometimes possible, even if getting a longer visa beforehand is not. This is obviously risky, but they would still have a couple of weeks to change their ticket if they get denied. (This assumes that they are not refused admission to Saudi if the immigration agent sees a return flight later than the visa expiration, but this is unlikely.)

Another exotic option, perhaps paired with the above, is to nest a ticket from Saudi to somewhere outside the country, e.g., to Dubai, such that their return to KSA is a couple of hours before their departure so that they can just transit. (One is supposedly allowed to transit KSA without a visa, according to the embassy in the U.S.) In any event, this would probably not be cheaper than the change fees you are facing.

Sorry, these are somewhat out-of-the-box potential solutions, but perhaps worth thinking about.