Of course the easiest way to hit the Sun would be to go towards the outer planets (from Mercury's orbit it would be harder to hit the Sun than from Earth's orbit).
Mercury's Mean orbital velocity (km/sec) 47.88
Earth's Mean orbital velocity (km/sec) 29.79
Mars Mean orbital velocity (km/sec) 24.13
Jupiter's Mean orbital velocity (km/sec) 13.07

From Jupiter it wouldn't require much to change the trajectory, but it's not very easy to get out to Jupiter (you would need a few gravity assists and would take several years to out there and years to get back). Gravity assists can increase orbital speed or they can decrease orbital speed, but generally the preferred way of describing gravity assist is that it's changing the vector of a trajectory.
If you are in a 300 km circular orbit above Earth, your orbital speed is about 7.7 km/sec. If you want to hit earth, all you need to do is change your trajectory so it intersects earth atmosphere: from a 300 by 300 km orbit to say a 300 by 50 km orbit. This doesn't require much delta-v (something like .5 km/sec). Btw, instead height above Earth surface, the orbital distance should considered from the center of Earth (center of gravity). The Earth's radius is 6,378 km.
You could probably fiqure out a trajectory which had a gravity assist at Mars, then coming back hitting assists at Earth, Venus, and/or Mercury which result in a trajectory which intersects the Sun (or if you want to miss it, get very close- you are going to burn up if you get within 10 million km of the Sun- unless you have some tricky ways of handling the solar radiation).