Mechanical keyboards are generally pretty pricey due to a number of factors. Typically the electrical design is a bit more complicated since modern ones will literally support all of the keys being pressed simultaneously if you plugged it in via PS/2 (if you tried to do that with a rubber dome keyboard it would shit itself), and there are way more moving parts. Rather than a flat grid with contacts on them, each and every key has its own individual mechanical switch. One plus is that you don't have to bottom out the keys in order to trigger the switch, reducing typing fatigue dramatically, and the other big advantage is that the keys themselves last a considerably long time. We're talking 20 million keystrokes for switches with a tactile bump (such as the Cherry MX Blues or Browns) and 50 million for linear switches (such as MX Blacks or Reds).
$140 is actually around the median price for a pre-packaged mechanical keyboard. In the case of he G710+ it's the MSRP. I was able to pick mine up for $110 (which, I should add, is around how much a typical rubber dome gaming keyboard costs). I'm also planning to buy two more fairly shortly, both from
WASD Keyboards--a CODE keyboard with MX Clears for work and a custom keyboard with MX Clears for my iMac. The rubber dome keyboard that I use at work is pretty lousy, all in all. The bog standard Apple keyboard is a scissor switch keyboard (think laptop keyboard). I don't normally mind those, but the keyboard has an aluminum back which causes me to bottom out hard when I type. One of my biggest mistakes was trying to play Cave Story on that system. Very ouch.
Oh, I also have another HAPPY thing. Got a fairly nice performance bonus at work, so I'm going to be grabbing a couple of GeForce GTX 980s here soon. It'll be my first-ever SLI setup. I was originally just going to buy one (since I have a buyer for my GTX 680 already) but what the hey.
Edit: I just bought two of
these. That...was 'spensive. Totally worth it, though.