Rival 100 is pretty cheap depending on where you get it, not really suitable for over 500 CPI as it then suffers from noticeable jitter issues, but is pretty comfortable, nice build quality for the price and has side buttons.
Ninox Aurora is a good mouse but you do run the risk of getting one that is made out of one persons will for it to stay together.
G100s is a good mouse but the build is pretty cheap, and you don't get any side buttons either.