Remarkable condition for a 1814 Copper coin. If it is genuine, this is what NGC estimates values at if slabbed and graded in USD. Of course your example is not slabbed and graded so judge from there.
Here's a way to guarantee the correct price. Put it up for auction starting at $0.99 and the highest bidder sets the price.
The problem with eBay is that it became a Retail market years ago. I just typed "Brazil 20 Reis" and their are 281 results of All Listings. Auction Only is 12 (4.3%) and your Type doesn't even show up (Also, never mind grade).
Good luck setting a price. Btw, you have a lovely coin particularly the die cracks.
It ain't what you don't know that gets you into trouble. It's what you know for sure, that just ain't so. Mark Twain
If you look at the attached link, you can see under the grading letters, two valuations, which is what members have paid for the coin.
Problem with the 1814 coin, in comparison to the other dates, is the high mintage.
Also, this coin, which looks very similar to your coin is on eBay. Only been on for 7 hours and already has a bid of £10.00
Put it in your watch items and see how it goes.
Maybe this has been discussed somewhere before and I missed it but I'm curious about the difference between the reverse of this coin and the one in the catalog. This coin has a reverse similar to the 10 Reis but different from the 20 and 40 Reis. Is this just a matter of different dies from different mints?