how to increase low end torque

[u mad?]

These things. Less weight in the car, larger displacement engine,

Those are your best bets. Start by losing weight (what you can justify anyway). Spare tyre, some sound deadening, rear seats if you don't usually carry passengers. Power steering and air conditioning if you can live without them, lighter wheels if you have heavy ones etc.

Otherwise every other option listed will probably cost you a good $3,000+

Final drive

I did these, happy with outcome