You may want to do an open search for the vent cover you are looking for. We bought 3 MaxxAir vents cheaper than the average price of the MaxxAir II. Often, the best price is not where you might expect it. And do it often, because the prices change quickly.
For instance, I found an item on Amazon at a really great price. Because we always discuss purchases beforehand, I took a few minutes to talk to DW. Went back on line to order and the price had jumped much higher. A recent eBay order was at a really great price. Having received the order, I decided to order more. The price had doubled with the same vendor. What I have learned to do when I see a good price is to get it into the cart to lock the price. If I find a better price, I go back and delete it from the cart. To do this on eBay, place the item in the cart. If you select "Buy now", you have committed to buy. On sites other than Amazon, I always use vendors that accept PayPal.