Erm, personally i will buy power (for now at least) its pretty low price atm, hovering about 0.11. With the 3 buildings you build (well, factory, gas station) i don't think you have much left to build your power plant.
I would (in long run) buy the power plant as well to maximize my profit, but for now, i believe just stick to that 3 building, prob get another gas station and see what you want to do from there. Or fast cash (i think) can just start the acc. with 3 gas station, can get all gas from the market

but dont think its a good long run strategy
Guess that's what makes this game interesting, you can try it out and see what happens
