Not sure if they're the cheapest, but you can get 30+ for $10 not including shipping of course. I've been thinking about starting a colony myself, but haven't just yet.
I just bought 250 mixed pair started kit wit 2 adult pairs... plus 5 extra males and 20 extra females for 75 buckss. That includes 5 egg crates a pound of chow and dry water crystals...from THEROACHGUY.com Jason was super helpful!
if you are genuinely squeezed for cash, then i think the cheapest ones are probably on ebay http://cgi.ebay.com/135-live-Blapti...emQQptZLH_DefaultDomain_0?hash=item1e5b4709f3 granted forum prices arent always the cheapest ones out there but when you buy from a forum sponsor or member, it helps encourage the future health and vitality of the forum, that should be worth something?