This one:
https://www.labor-bayer.de/ But get the price confirmed first again, some minerals tested are bloody expensive. Tested it last a year ago, at which time that price remained stable already for 6 years. Usually I test it together with potassium, iron, zinc, copper, lithium - all in whole blood, and all about the same price. Also test stuff with them a bit more expensive (€24,--38,-) but not available through my GP, like CoQ10, retinol and RBP, methylmalonic acid, GSH-Px and SOD1.
I get the blood drawn at a local laboratory in Austria and they send it in. And don't have to pay for the blood-draw itself, since I come with a referal from my GP for homocysteine anyway.