I always use live mealworms, though my local pet shop sells dried ones at £3.89 for 500ml.
However, it seems that some birds are fussy about their food! I know several people who have bought
live mealworms for their bluetits, and they were completely ignored.
My sister-in-law bought a large tub of dried mealworms and they've been completely ignored - she said she was going to throw them away, but I've said I can use them in my home made suet blocks and fat mixes, I'm sure they'll get eaten that way.
I suggest you buy a small quantity first, to see if your birds will take them.