I suggest using the more advanced money system. That way you wont get the same amount of money for killing a zergling and the same for an ultralisk.
The tutorial link is here.
Kills to Cash 'Perfect'[right][snapback]144677[/snapback][/right]
If you had checked the links that linK_ had posted, you would've realized that he already posted a link to that tutorial.
Also, his question was about getting 1 mineral for every kill, no matter what unit it was. Please read the first post more carefully to see the question better next time.