yeah, check for termites, carpenter ants, etc.
The repairs are possible.
In general the process is:
remove damaged boards
install replacement boards of same species
sand entire floor
refinish entire floor
Before that you would put a proper threshold and sweep on the door.
Costs? It will cost what the market will bear in your area. Get three quotes from reputable flooring contractors for comparison. No way to say what it would cost from here.