The test was:
$40. For the post
$30. For culture for blackhead
What should I be feeding them?
Something specifically formulated for their species is best, but many grower feeds are applicable across the board for a few species.
It should say somewhere on the bag that it's indicated for certain species, within certain age groups, intended for certain purposes, i.e. you feed future layers different feeds than future meat birds.
Different breeds have different needs, as well.
If you're getting a preprocessed mix that doesn't clearly indicate what it's intended for, or what nutrient levels it's expected to have, this can be much more difficult, in which case it can help to look up the basic nutrient levels and types the species, age, and breed needs, and calculate your own formula and premix it yourself from separately purchased ingredients. Plenty of people do that, I used to in the past and intend to again... But it is quite a hassle for some. If it's too much trouble for you, it may well be worth the potential bother of finding a specifically turkey-food mix.
Layer pellets are best only fed to layers; sometimes you get away with feeding it to non layers for long periods of time but plenty of people also don't get away with it, and suffer losses and general disease.
As for the test cost... Might be worth it, but if you're going to the bother to send off a corpse for testing, personally I'd want to know what it IS, not just what it ISN'T --- are you going to get that sort of info from them? Some kind of general diagnostic testing rather than just testing for one single disease may be better, but I don't know how accessible this may be to you.
Anyway, best wishes with it all.