Recommendation for very simple character customization?

I'm part of a project building an RTS game with RPG elements. The units are small and numerous, as you'd find in an RPG, but they can be upgraded as time progresses (new armor, etc.) The upgrade system is rather in-depth, and building separate models to account for every conceivable combination of upgrades would take entirely too long. Is there a way to implement a simple character customization system (I'm thinking along the lines of Runescape) where you might have 4-5 slots for different things (maybe 3 slots for apparel and a slot for the unit to hold something). Ideally, changing an accessory would cause a visible change in the unit.

The character customization assets I've seen (Fuse, etc) look nice but seem awfully over-powered for what I need, and I'd hate to spend $50 on something I'll get 5% of the functionality out of. Being that there might be a good handful of units on the screen at once, I'd prefer something simpler that will have less of an impact on performance.

That being said, my units are all Mecanim-run, so I have to stick to using a skinned mesh with bones as my base. I appreciate any input!!