Helmets r us has been a good source for cheap helmets (rated helmets starting at $4 for non-profits). I've known of a few sources for free helmets in the past, but those I'm aware of have moved onto other health related causes.
Otherwise we use sunlite ulocks via JBI bike (aka j&b) which cost about $6.5 (up from 4.50 from our first big order). We've also gotten a ton of lights on their close out list which we provide if necessary. Their kidzamo line is a knockoff of knog's style and cost on front or rear lights is $3, as I recall.
Hope this helps someone, but would gladly have a different source for any of the above!