i completely agree with what has been said. It is very cost efficient, and only becomes better with more snakes. At the moment i've got 7 females for breeding (i plan on adding 3 or 4 more so i get a bit of excess) and have built a rack and everything. and even taking into account the initial materials cost and the first bunch of rats, that gets recuperated in a fortnight, and food is probably weekly (considering i would be buying $70+ of food every feed if i bought them from a store) so if you feel like you have the time to do it, i say go for it mate
oh and yeah, i use the sodastream method too, it works great and isnt that dear (of course dearer than a knock to the head) but is a bit better if you have an issue with that/