Budget minded upgrades:
Start with the HD front sway bar and rear sway bar
Step 2 grab the cop/300/big block torsion bars
Step 3 good parts store shocks or better
Step 4: 5 leaf rear springs

This will make a nice cruiser. My old 300 that now gets autocrossed has a very basic build. Biggest upgrade on that car is the 16x8 wheels and the tubular UCAs and boxed LCAs

1971 Challenger