There are so many asteroids. To move a large asteroid, like cruithne to Mars, you don't have to do it directly. Small asteroids could push larger asteroids slightly to collide with even larger ones, until a larger one is cought by a gravity well.
Rather than investing $ to lifting more fuel, it could be invested into getting more information -- surveying the surfaces, masses, spins, etc. of asteroids to make precision collisions.
Inspired by [asteroid to mars] idea.-- Inyuki, Aug 02 2012 zevkirsh's idea: "astroid to mars" astroid_20to_20mars [Inyuki, Aug 02 2012] Simiar, perhaps more general! So, better! Asteroid_20collider [Inyuki, Feb 18 2019] I think you'd want to do it by gravitational slingshotting rather than by collisions - the result of a collision would depend too delicately on things like surface topography and spin.-- MaxwellBuchanan, Aug 02 2012 Okay, so it is what I thought. Bun in the corner gravity well.-- Alterother, Aug 02 2012 I feel the problem would be getting a piece of green baize big enough.-- not_morrison_rm, Aug 05 2012 ...and let's not forget about the chalk. Where are you going to be a 1km/2 piece of chalk? If suddenly the white cliffs of Dover ain't there any longer, we'll know where to point the finger..-- not_morrison_rm, Aug 05 2012 Sounds like the cue for a pun ...-- 8th of 7, Feb 18 2019 It Oort to be alright?-- not_morrison_rm, Feb 18 2019 We don't want to comet on that remark.-- 8th of 7, Feb 18 2019 random, halfbakery