I'll try to find some numbers tonight comparing going to the moon, using the moon for a slingshot, and what it would take to go to an NEO.

Going from LEO to GEO is a special case, at least for satellites launched from places other than near the equator. It actually takes more propellant to put a satellite launched from Tyuratam (Balkinor) into GEO than it does to send something to Mars. This is due to the energy required to lower the satellite's inclination from about 51 degrees down to near zero degrees. Orbital plane changes require a lot of energy.

Several years ago, I saw some numbers for the Russian Proton booster, their workhorse for LEO, GEO, and Mars missions. The base Proton can put roughly 20 metric tons into LEO. To put an object into GEO, you need a big upper stage to both raise the orbit and lower the inclination. The Proton can put (according to the old numbers) 2 metric tons into GEO. However, it can send 5 metric tons to Mars! The reason is simple - it takes that much less energy (3 metric tons of propellant worth) to go to Mars than it does to go to GEO and lower the inclination to a usable value.

That's why the moon swingby missions were used to salvage that satellite a few years ago. The upper stage failure had left the satellite in a highly eliptical orbit that was way too inclined to be useful even if the satellite propellant was used to circularize the orbit. It didn't take all that much additional velocity to boost the satellite out to the moon where lunar gravity could be used to lower the inclination. After that, the satellite's fuel was used to circularize the orbit. Pretty damned clever IMO!