It all depends on what has been done, how well kept the car is and what you plan on doing with it.
Few random thoughts...
Find a deal for 10K less than average and you can easily drop 10K back into it.
These cars are getting older and the selling prices are ever widening.
If you find an example...post up some pics / history and lets take a look.
Personally, for what I use my Viper for...I wouldn't have a problem dropping 60K on a prime example and running away as fast as I can with a 40K car.
If I were to track it...then maybe that 40K car might be more attractive.