Micro Loader by Bangoo H. Replace the minifig parts
with a head and this could make an interesting frame.
LT-VMI Gunner by Arcandio. Simple, straightforward,
nice. I think a squad of these guys would be pretty affordable.
He even has a set of weapons to go along with it.
01-GD Charger 1 by Gobboleone. This looks
like a riff on other designs we've seen.
Hammerhead Worker Mech by Gogglez. An interesting
variation on Ironsniper's Hammerhead mech.