this is a very good way to produce food for those use nightcrawler or red wiggler(red worm) as staple food source, especially for those who cook at home a lot. i gathered some information online and a little personal experience from composting. $5 for 20 worm is actually a lot cost if you add it up, yet breed your own cost almost nothing after the starter.
under idea condition, they should double in number within 3 month. if you are taking them out for feeding along the way be sure to have more starter worm. red worm produce more rapidly than the rest but it's the smallest. personally I use european nightcrawler, slower breeder but full size about 5" good for my pacman. (both canadian and africa nightcrawler are even bigger, but they are more picky on living condition)
to set up you just need a container/lid that's big enough to hold them, substrate, food, spray bottle, and of course your starter worm.
container
they dont really need that much space to move around. I'll say a 20qt plastic container with cover is good for 1~2lb of worms. there are ROUGHLY about 100 european nightcrawler each lb. I am not sure about red wiggler, but they are about 2/3 of the european one so guessing around 150 worms per lb. they actually produce better if living together so just get a bin large enough for the amount you need. it's better to go with the surface area other than depth so it's easier to search for worm.
substrate
the basic idea for substrate is it should be chemical free, not muddy when wet. You dont want the substrate build up too high that it takes forever to search for worm, and it should be damp but not watery. I use the eco earth that's cleaned out from my frog's tank, which is perfect. As time goes you'll see it builds up cuz they poop a lot too. Their poop looks just like dirt, which is the best organic fertilizer, dump them into your garden or your lawn if they build up too high.
air
if you keep the covers on and there's no hole on it make sure you open it daily, and leave it open as long as you are around. They do try to escape when they first move in(having a light over it helps), or when the condition is not so idea. They need to breath through their skin, which is why dont use muddy substrate. Air flow also helps get rid of the smell and lower the chance of mold building(not like the worm really cares about mold, but it's just looks nasty).
water
Drill hole at the bottom helps get rid extra water but not a good idea if you keeping it indoor. What I do is just flip through the bin as I feed them or looking for my frog's dinner to make sure it's wet enough, which is also why it's good to keep some dry up substrate at the side in case if there is too much water at the bottom. spray it if not.
food
they will eat anything that ever lived(organic), but DONT use meat, dairy, acidic food like lemon or oily food. those will start smell bad really quickly and attract unwanted visitor. table scrap, vegetable peel, left over salad, leaf, even the grass cut down from your lawn will make them happy. Try not over feed them too much, one big reason the bin smells bad is because of overfeeding. also note some vege (especially fresh one)contain a lot water, becareful with the moist level when using them.
Temp
keep them at room temperature is fine. they could survive a very wide rang of temp but i'll say the best result are around 60~70. the bin starts to smell bad very fast if it gets hot.
it's really cheap once it starts running. the only things cost money are the bin($5 for 32qt @walmart), and starter worm(got it for $30/lb free shipping within US), nothing cost money other than that.
hmmm...I guess that's it. I am also learning as my bin grows, let me know if I miss anything, and again sorry for the grammar error lol =)