i wouldnt feed rats or chicks to hatchlings, in fact, not i wouldnt, dont. feed the snake mice until its fairly big. then try rats, chicks aint small, i shud think only adults could eat them. but thats me. feed mice till about 1 year old +, then rat pups + small mice then upgrade along with your snakes growth. but id feed chicks wen the snakes very large.
anyways in answer to your question, rat pups are around 40p around here, pinkie mice are around 30p chickes r 15p, small mice are 55p
but dont forget, mice are VERY good for the snake and are full of calcium
rats are very fatty for the snake and dont have as much goodness as mice
i dont know wot chicks have apart from shapr claws which i wouldnt give to my snake. if he eats it backwards hes pretty much doomed