Hi jessmarch,
The first thing I would normally do is call the manufacturer who will usually have a replacement cover they can sell you for much less (and sometimes if you have already purchased from them they may also offer a lower price). If your quote was from from the manufacturer themselves though … then I would look at alternatives because this seems very costly to me (although I don’t know the details of the cover).
In that case … some of the better sources of good covers of many types are listed in the toppers and components post #4 here and they are also significantly less than $1000…
Phoenix