Sure,I'll help you
Any soil that they can oviposit into is probably fine.They do it in the wild.I use coco fiber because it's cheap,clean,free of parasites, holds moisture well,and has worked fine for me.For the cup of cocofiber I use the smallest delicup which is the 8 oz cup I believe(it's only about 2'' high).The key is to keep the "dirt" damp but not wringing wet.You can watch the females stuff their ovipositor into the dirt like a sewing machine and they will lay the eggs in the cup constantly.You will be able to see the eggs jammed against the side of the cup between the substrate and the cup.Change the cup every 10 days or so with fresh dirt or they may eat each others eggs.If it dries out, the eggs will die.If it's too wet,they will die,but if kept damp,they will thrive.Most leafy veggies will wilt and mush pretty quick.They love apples but it will rot quick too.I like to use the squash because it lasts longer,and really isn't expensive.It's really easy to grow too if you're into that which will make it that much cheaper and will keep for quite a while in the fridge.The flukers is fine.I raise chickens and get a 50 lb. bag of high calcium layer pellets for about 13 bucks.I have to buy it anyway. I just run it through a coffee grinder (yard sale pickup for 2 bucks)to make it a powder.I use the powder diet (or in your case flukers which is fine) and the squash in conjunction.The powder diet gives them the calcium rich dry food they need and the squash/zucchini for added nutrition,but more importantly for the hydration factor(very important too).The added nutritional value is an added bonus,but beneficial.Squash depending on the time of year can cost $1 per pound or 3-4 for $1 in season.I get mine from the local flea market which is fresh off the farms and even cheaper.If you know anyone that plants a garden,often they grow so fast that sometimes they grow larger than people like to eat and throw them away.I try to grab those too.They are just fine for crickets and roaches for that matter.After you have success with it,it's pretty easy.True pinheads (you usually can't buy)are super tiny.Smaller than melo ffs,but they do grow pretty quick.Sorry if this is too wordy.