UPDATE: Looks like the price at B&H has been changed back to $299. Amazon is no longer showing the item available for preorder.
The EOS R system will be available for pre-order at midnight tonight, but it looks like there are some price mistakes you can take advantage of right now.
The Canon Drop-In Filter Mount Adapter EF-EOS R (Circular Polarizer) is available for pre-order at B&H Photo Video for only $99.00 — save $200 from the regular price of $299.
It’s also available for pre-order immediately (no need to wait until midnight). As this is likely a price mistake the orders may get cancelled, but hey, it’s always worth a shot!