The problem is that your proposal as phrased is, in terms of orbital mechanics, gibberish.
First, you can’t shoot something past the sun in order to accelerate it in the sense that you mean. Don’t get me wrong, the sun accelerates things constantly, and moving something closer to the sun will increase the acceleration it derives from the sun, but that acceleration is mostly acceleration in terms of altering the direction of travel and not in terms of making something go faster or slower relative to the earth. You can’t use the sun’s gravity well to do any kind of gravitational slingshot in the way you’re thinking - the sun’s gravity can’t alter your orbit around the sun, because that’s what your orbit is. You need another gravity source that’s moving relative to the sun.
Second, the delta-V requirements to fire something close to the sun are ridiculous. You basically have to cancel out most of the earth’s 30km/s orbital velocity. Then all you’d get is a highly eccentric orbit, and assuming you calculated correctly and that your projectile arrives back in the vicinity of earth, the encounter would be best described as the earth running into the projectile rather than vice versa. In this case you’d be better off expending the ridiculous amounts of fuel you burned by accelerating straight at your target.
Third, if you really want something to be moving at very high speeds relative to earth you’ll be best off using Jupiter’s gravity well to set your projectile onto a highly eccentric orbit that crosses earth’s orbital path at roughly right angles, which should get you into that same 30km/s range while having only expended a tiny fraction of the energy.
Really, you’d know all this if you played Kerbal Space Program.
Michael Bay covered this in one of his documentaries. The Constructicons combine for form Devastator, which is able to shred that puppy to reveal the Sun Harvester.
No miners here? Just drill blast holes in a 10m x 10m grid through the whole thing, pump in ANFO, stand back a safe (very safe) distance and boom! Sorry, the thing won’t disappear. It will just collapse on all sides into a pile or broken limestone.
There’s an old saying in the Marine Corps: Lock two Marine Privates in a windowless concrete bunker, with nothing but an anvil in it. Open the door an hour later, and you’ll find the anvil broken and both Privates missing.
I’ve heard the Army has a similar saying as well.
So on that note…
A full battalion of Army and Marine Privates and PFCs - over a thousand of them. Bus/truck them to the pyramids, tell them not to touch the pyramids, then leave them there, with no adult supervision. Come back in a few hours to a few dozen Privates throwing fist-sized chunks of pyramid rubble at each other because they’re bored.