We bought four fans at the dollar store and they were totally worthless, threw them out on the second day. They kept coming apart.
Broke down and bought the WDW misty fans. Within an hour the first one broke, no fault of the kids. DH took it back to a stand where they replaced it immediately. An hour later another one broke. Again, DH took it to a stand and the CM replaced it and said if it broke again to take it anywhere and they will replace it.
We ended up replacing about 5 fans over the course of the trip, in all 4 major parks. We didn't have to even replace the water in either of them until the last day because they would break before the water ran out! The good news, at least, for the $17x2, the kids always had a working fan!