Can you afford an automotive electrician? How is the rest of the wiring on the car? Might be worthwhile getting it to an expert if you can afford it, or ask all your friends if any of them are better at electrical.

Could be lots of potential faults ar even multiple problems.

Are you sure the battery itself is still good?

Fuses and Fuseable Links?

The Firewall Connector?

The Alternator and/or regulator may be fried.

The Ignition switch or Starter Relay, dirty Battery Cables, Bad Grounds, etc.