2 PCI slots (1 available) •1 PCI-E x16 slot (available) •1 PCI-E x1 slot (available)
So I don't think anything over $100,- will increase your performance due to your PSU/mobo not being able to fully utilize it. Possibly less.
What is your location? Quoting newegg won't be useful if you live outside of the USA.
Relevant: Someone in motherboards is trying to upgrade a computer closely related to yours and is running in to a problem that might be applicable to you as well. Hasn't been solved, might be worth keeping an eye on.http://www.tomshardware.co.uk/forum/323188-12-pcie-slot-dead