Bhai what are you smoking I want to know. The reason for an 84 Civic being of RS. 150000 is because the owner can't keep it good, the interior is efed up beyond repair, the engine is on its last breath, the body needs to be restored if possible, you can't run the thing on petrol let alone you want the AC to work. The only advantage is that it is CNG and a sedan means bigger space.
I am not writing this to hurt your feelings but I own a well kept 80s car and I know what it takes to restore them.
When these Civic came out new they were brilliant vehicles but today with the jugaadi culture she has been ruined.
You can buy it as a daily runner to keep it in as is condition and change it when ever you have sufficient money. But when buying Rust and Mechanics Condition should be your priorities.