Many programmers believe that most any keyboard/mouse will do whenever it comes to doing their job. While it will get the job done, in reality some "cheap" hardware can end up costing you a lot of time and effort.
In short, it is the little things. Things such as key spacing, the responsiveness of keys, hand positioning, etc. all end up costing you more than you might think. For example, what if you could save .2 of a second per keystroke, by simply switching your keyboard to one that is easier for you?
Doesn't sound like much but lets do some math. Lets say, you make
5000 key strokes a day in a standard weekday. So that is:
(5000*5)*.2 which equals
5000 seconds OR
1 hour 23 minutes and 20 seconds.
That means, every week, you could be wasting about 1 1/2 hours at work, that you don't have to.
Additionally there is the comfort of the device. The wrong keyboard/mouse can leave your joints/fingers aching.
What is Best
Now the most expensive keyboard isn't always the best, and more importantly isn't always the best for your particular situation.
I am someone who likes to code in the dark, and I also spend a lot of time in Photoshop so I like pen tablets, but I also don't like how the pen sometimes makes my wrist hurt. So my keyboard is back-lit, and I have a trackball mouse and a pen tablet that I switch between frequently. I really don't care for ergonomics, because my wrists have never bothered me, but that whole wave-keyboard-thing does.
For me, my setup is perfect. But for someone else, it could be really bothersome and even painful.
For my setup it cost me around $150 to get everything new, and to be honest, I have yet to have a day where I regret spending that much. Now in most cases you won't end up spending that much, more or less because I buy more expensive things simply because I want them and can afford them. (ok I might be spoiled)
I would imagine you could find a good setup (assuming you get just 1 keyboard & mouse, I prefer Logitech) on eBay for around $45, maybe less; while a brand new good setup might cost around $75, depending upon where you go.
In the end, you may end up spending more or less than you originally planned (preferably less). But even if you do end up spending more, this is one of those things that just proves its worth over time.