Itsy Bitsy Spider.
Security Droids.
All with using cheap Ebay GW stuff or traded bits.
Though I'm desperately short of Space Marine Vehicle Missile Launcher or whatever it's called, I'm looking at finding another 4-6 of those launchers to complete the entire swarm. (So if U have any spare, or wish to sell, PLEASE!!)
Coincidentally, they make good 6mm sci fi craft too
The Spiders are easy, and not too expensive on Ebay, or just buy a Goblin Dwarf Pass something box from GW and sell off what U don't need. Just repose em and that makes em look a lot better. IMHO ofcourse
Johan