I'm curious what you mean by how much you "invest". Do you mean how much you pay for it? Isn't .com $13 in most places? Or do you mean to say you spend a couple k from a broker? If it's the latter, I'd hope you're prepared to be serious and focus on developing it.

I refuse to buy domain names from speculators. I think it's one of the scummyest (legal) things you can in relation to the internet. You're buying cheap resources on the hope that someone is desperate enough to give you more money for it later. They're middle men that provide no service and add zero value to the world. They're just selfish.