You can get a nicely done 383 4 speed 70 Challenger R/T for around 30-35K today. This is traditionally the best time to buy a collectible car, and the worst time to sell one (Christmas/Holiday time has always been like this). It's a buyers market out there now, so buy before B-J at the end of January.
You did not say what color the car is, and that can make a sizeable difference in it's market value. Original high-impact color cars bring a good 10%-20% or more than the less desireable colors. Also, any other "good" options? (Rim-Blo, AM-FM, rallye cluster, cruise control, power windows) All these options add to the value, especially if documented with a fender tag or even better, a broadcast sheet.
From all that i read in your description, what you are describing is a clean driver type car. Thats a 30k car today, maybe less if those SE pieces are missing. They are hard to find and bring a premium $$ wise.
Good luck on your search
