Bt isn't any more expensive than the harmful products that people often use. The trichogramma wasps should help, but 3000 doesn't go far, considering their size. I would go with the Bt, use a sprayer that hits as much of the plants as possible, but be careful not to broadcast it further or you'll harm butterflies.
Bt comes in powdered and liquid form, in this instance, the liquid in a hose end sprayer, per instructions, shouldn't amount to much of a cost. Thuricide isn't an expensive product and it would only be part of a bottle, I'm guessing.
Last year's spring was a sight to behold - a disaster to many gardens throughout the region. This year seems to be shaping up to be a better year (though the hail that hit a few weeks ago smashed a number of my bedding plants). Bt works when the worms are feeding, it interferes with digestion. Pick what looks like a dry spell of a few days and spray on the first dry day, giving the bacteria time to work in the guts of the caterpillars.
https://en.wikipedia.org/wiki/Bacillus_thuringiensis