even though 71 is not the most desirable year for the charger, it is a model that is coming into its own. The 68-70s are harder to come by, so people are looking to the 71-74s as a lower cost alternative.
the 318 is the least desirable engine for that car. you can go as high as a 360 without replacing the K-Frame and tranny. If you step to a 383 or higher, you need to swap the K-Frame. Its not a big deal to do, and there are plenty available at dismantlers like Mopars of Texas,
Rust is what worries me. if the trunk pan has rot, then you can bet the floorboards do too. Sure, you can get repo parts from Year One, but rust repai is something that takes a lot of time and attention to do right. Do it wrong, and you will be chasing rust forever.
for a car with a small block, rust, missing parts, and no starter - 1500 may be a tad high. I might go as high as 1000, but even that would be a stretch IMHO