No no, they are perfectly stable - I use 3x2mm in the suits, and 2x1mm in the guns. Using paper clips would be an option, but I like the fact that the guns themselves are magnetised so they can be stored stuck to a flat metal sheet.
It doesn't take too long to do, but in any case the 43 bits are going to be enough to service 9 suits in the end not just these 3!
As for cost it's very minimal - from ebay, a pack of 50 or so magnets is very reasonable.
How hard is it putting magnets into things?
Not hard, I drill a hole slightly too small in diameter, then put a dab of superglue on and force the magnet in (hammer it in with the butt of a pen, or squeeze with pliers). Holds like a charm - in fact I doubt the glue is even necessary.