Guild Wars 2

I am at nearly at 700g and I was wondering is it better to just buy dawn or use mystic forge?

Totally depends on whether you want to take the risk or not. You are close to getting a guaranteed Dusk by just buying it. But with a little – maybe a little more – luck, you can keep all your money and get Dusk from the Mystic Forge. Or you could loose it all and regret your decision.
I can only tell you, what I would do: I would choose option c) and wait until precursors become craftable.

I would suggest to buy it from the tp. Recent research has shown that the prices on the tp are quite in line for the average amount of exotics you will need to toss in the forge to get it.

You might as well spend 700g on the moa races.