Not sure what this is just a decorative piece maybe? Or maybe something with some value?
Solid brass Trojan/Gladiator helmet used for display/decoration.
There are 2 helmets like yours listed for sale on eBay but none have been sold for several months/years? so without a sold item, it will be difficult to place a value on this item.
Also, your helmet looks to have some damage which would also take away from the value as those spots will not polish out.
We have no way to know how long the 2 listed helmets have been up for sale - maybe weeks - maybe years.
eBay's for sale listings:
This brass helmet looks very similar to yours and is listed @ $495:
This one sold for 500 British pounds onlineonly.christies.com/
Does a magnet stick to it? If you ping it with your finger does it have a bright sound or a full sound? Can you give measurements or add something like a soda pop can to give an idea of size?
This is a vintage 1970's solid brass Trojan helmet statue/bookend - for decoration, not for wear.
The price of two looking identical but in excellent newly machine polished condition vintage solid brass Trojan helmet bookends (8" tall, 8" deep and 5" wide) is $475 www.chairish.com/
The price of another identical looking vintage brass Trojan helmet with patina is $89.95 www.ebay.com/
So in this condition, as it is now, the price of your helmet is about $80-90. Polish the surface of your helmet and its price will be higher.
I found a very similar vintage solid brass helmet - Trojan Spartan Gladiator www.ebay.com/
The price is $90.
Someone already sold another vintage solid brass Trojan Spartan Gladiator helmet i.ebayimg.com/
There is a similar one online , under $40 . Right now you could make more for the brass itself.www.bing.com/