mines are always on same spots, everyone can predict where they are, but also have fear to risk to see.
I agree mines is cheap as fuck, the price is not a problem... almost 200 RU for a mine lvl 3, but if someone step in your mine, you recover almost all RU used for build it, so, most of mines are almost free cost.
Same for SM... SM is an investment, because you always gain more RU than spend for build/up it.
the costs are fine, but rewards are crap