What would it take to replace the Anti theft system, or ignition in this car?

try another key 1st thing

There are video's on youtube showing the bypass procedure. Suggest having a locksmith take a look at it. Did you try cleaning the key? Do you have another key?

Whole system would not need to be replaced. Components of system can fail or wear out. Need to have it diagnosed and repaired. Common fault is the ignition lock cylinder has very small wires going to the part that senses your key and break with age. New keys with a replacement lock cylinder are the most common repair.