Seamless Group Photo Composite

I have two high-resolution images: a solo portrait and an outdoor group shot. My goal is to isolate the person from the portrait and place them into the group photo so convincingly that no one can tell the image was ever altered... (Budget: $30 - $250 USD, Jobs: Adobe Lightroom, Background Removal, Digital Art, Graphic Design, Photo Editing, Photo Restoration, Photoshop, Photoshop Design, Visual Effects)