im sorry you've been having such a rough go with the crickets! I was buying from a local pet shop for my leopard gecko and they cost 8.50 CAD for 50 crickets, and over 15 of them would be dead at the bottom before i bought them, and then the rest would die really quickly in a day. i can only assume the crickets were just poorly cared for in the pet shop, or they took too long to get sent out and ended up dying. I buy small crickets from pet smart currently and in the past 10 days i've bought over 300 of them, and i've had maybe 4 end up dead, which is excellent. i ended up buying my large crix there too for my leopard gecko and i wanna know their cricket source because they are so hardy and feed well, and i havent lost a large one yet!
im really sorry you've lost out so much money as i know they can be a costly thing for a small fella like you have, i feel for you there. i hope you have better luck with the worms, maybe you can find a better source for your cricket purchases. But if they keep dying it could be something in your home causing it, that you dont realize. Very strange. Best of luck, though!