Power is not a problem, divergence is. You would need large optics.
Formula for spot size at distance is:
spot_size = distance * wavelength / aperture_size
and you can derive from it:
aperture_size = distance * wavelength / spot_size
All values must be in same units, preferably metric.
Let's say you want spot size 1mm. Let's do it for green, which is in the middle of the visual range. Let's pretend yard and meter is the same.
That gives us:
spot_size: 1mm = 0.001
wavelength: 550nm = 550*10^-9
distance: 700
That gives us 0.385m aperture size. That's one big telescope, costing $1000 or more.
At 1mm spot size 200mW should pop balloon easily. Increasing power would could help you, but just a bit. With half the size, you could get spot twice the size .. but for the same burning capabilities you would need more or less 4 times more power. So with just a pointer, which usually has aperture size about 1mm, you simply have no chance. Even with 10cm telescope (which I have) I would get spot about 4cm large at that distance. It would require several watts to pop the balloon.
Btw. that's why ABL, the airborne laser, in my avatar, has 2m output aperture.