For a basic 500 square feet project in zip code 47474, the benchmark cost to Insulate Your Home ranges between $0.63 - $1.43 per square foot* . To estimate costs for your project: 1.
So in answer to your question, the oldest fossils are stromatolites, and the life forms that created those fossils were prokaryotic bacteria and algae like cyanobacteria.
Multicellular animal fossils and burrows (presumably made by unknown, soft-bodied multicellular animals) first appear 700 million years ago, during the Vendian time. All known Proterozoic animal fossils had soft body parts: no shells or hard (and hence preservable as fossils) parts.