One of the websites I frequent has a sale on glowsticks this month.
$2 for 8-12 hour Milspec glow sticks in red/orange/yellow/green/blue.
While not the cheapest option out there, it's nice if you absolutely -have- to have a specific color.
I know I've gone hunting for just Green glowsticks in the past, and had to break up multi packs to get them.