Scanning for asteroids is pretty simple in this round of Planetarion. You can calculate the actual probability that a astroscan will succeed
here; in general, the probability never drops below 30%.
Since each astroscan costs 2000 Crystal, you get one asteroid for about every 6500 Crystal - at least.
If you build wave amplifiers in a clever way, your cost per detected asteroid is much lower. (Again,
use the calculator.)
The initialization however quickly becomes expensive. You may wonder when the asteroid will return your investment.
Well, it is pretty easy if you think about it, but to make it even easier for you, I put another small calculator
for that here.
An asteroid is "amortized" when has produced as much as it has cost you, and from that point on becomes profitable. This is also called "break even point".
For other asteroid types (crystal / eonium), there is no such direct amortization, because you can't initialize asteroids with crystals or eonium. You may estimate what ratio you would trade metal and crystal/eonium, and try that.
We'll put up a small calculator for that soon, too.