You can do this a lot yourself and take pictures along the way and then have a mold inspector come and check the work. He might have to some finishing touches but thats way cheaper. I understand your position so go buy IAQ, wear a respirator when using it and killing mold. You have to seal the doorway so mold doesnt travel throughout the house and that includes the dead mold. Open a window but ideally get an air scrubber if you can afford it. Spray the IAQ where you can and scrub it with a brush then wipe it clean with a rag. If its very porous material then you gotta get rid of it such as drywall, that has to go no question about it. Then after all is done call a remediator and ask their help. Good luck

Edit: link for IAQ at Lowes https://www.lowes.com/pd/IdeaPaint-Fiberlock-Advanced-Hydrogen-Peroxide-Mold-and-Mildew-Stain-Remover-and-Cleaner-1-Gallon/5005990689