I have G15 keyboard and there are a couple of reasons I could see for spending extra on a keyboard. One is extra features. When I bought the G15 I was playing a lot of WoW and the LCD was actually very useful as were the extra keys on the left. The other reason would be for higher quality. Buying 1 $100 and having it last a couple of years rather than constantly having to replace $20 keyboards might be cheaper in the long run. If you game a lot your keyboard can take a real beating which is why I don't use wireless keyboards for gaming anymore. They are too expensive and don't last as long as standard wired keyboards. But ultimately it comes down to comfort. Whatever feels best for you is what you should use.
I got to 2300 rated arena with a 10$ mouse and 20$ keyboard in WoW many times... I would strongly argue that cheap keyboards don't last long.. I'd bet nerd rage would end their life pretty fast though.. I never EVER buy good stuff.. Heck the brand on my keyboard is like Mii or something.. super cheap wal-mart special but has function keys for media player etc... works great, and has for years.. Now the dell keyboard it replaced was another story... On the mice thing.. I use logitech, always have, always will... the cheapest still has good quality..
SO no OP, don't spend 100$ on a keyboard... Spend it on hotpockets...