You have to look at total cost of ownership if you really want to compare-insurance, maintainance etc then divide by amount of time you had the car.
I.e. car cost me $20k after trade-in, had it 48 months, so it cost me $416 a month of ownership, compare to what the new one will cost, how long will you keep it.
The shorter you keep a new car usually costs more since you have a lot of depreciation first 3-5 years, tapers off after that.
Now: 2016 Mustang GT Fastback-Magnetic Metallic, Ford Racing Touring axle-backs, Ford Racing front strut and k-brace, K&N CAI, sound tube delete, 1975 Corvette Coupe-L48, 4-speed
Past Lives: 2001 Corvette Z51 Coupe, 2012 Mustang Grabber Blue Coupe, 2008 Mustang Torch Red Vert, 1988 Mazda RX-7 Vert, 1985 Nissan 300ZX, 1979 Mazda RX-7, 1971 Datsun 240Z, 1972 Fiat 124 Vert, 1971 Chevelle, 1970 Challenger