Roughly ten years ago, when I first started living on my own, my life was simple. Every aspect. I stocked shelves at the grocery store to pay my bills. I had only a bicycle for transportation. $25-$40 a week for food, with about $15 a month of wiggle room in the budget. So the only possessions I had that weren't clothes (and two of the usual types of dishes) for the first eight months was my desktop computer that I gamed on, and the desk and chair for it. Buying cheap in those categories taught me about ergonomics the hard way.

No computer chair that retails for under $100 will be comfortable for more than an hour or two. None!

Then there was the mouse I was using. Which gets me on-topic... Sorry for rambling lol. I was using a Labtec optical mouse that had to have retailed for $10-$15. It is not suitable for more than occasional use.
Name: s-l225.jpg Views: 73 Size: 5.5 KB

That mouse caused nearly crippling pain to my wrist. The hand position itself wasn't horrible, it was the shape. The sides just slope down. You have to apply a lot of grip with your non-clicking phalanges when you need to reposition the mouse on the pad.

Mostly being a gamer when on the computer, I despise wireless peripherals (dead batteries & lag). The ergonomic mouse I bought (right before it was discontinued!) was the Logitech G5 laser mouse.
Name: g5orange-top-and-left-side.jpg Views: 73 Size: 35.2 KB

Name: g5orangebottom.jpg Views: 76 Size: 12.5 KB

This was in the $50-$65 range. It fits the shape of your hand very well, IMO. And you can even customize the weight of it!

G5 Laser Mouse - Logitech Support

I don't know if they have an ergonomic version, but a keyboard I was lusting over (before my PC was too obsolete to game on anymore) is called "Das Keyboard". It is a device that can be abused, and still work!

Das Keyboard - The Ultimate Mechanical Keyboard Experience for Badasses