Prabhojit, I've owned an SS80 in mint condition for many many years and sold it in 2004. It was one of my first cars. Although they are a joy to drive there are many things about the SS80 which are a pain in this day and age.
To start with you can't find any body panels / and the sheet metal on this car is fairly thin. The A pillars, firewall, all Fender corners (where the mudflaps mount), the bottom of the front doors, the rain channels are all prone to rust however well you do try to primer and paint the car.
The original Mikuni carb packing kit, is a pain to obtain in the market as are little things like the indicator lights, tail lamps and the front grille. Forget about interior parts! I took two years to find a rear strut for the bootlid glass!!!
You'd get an okay car for as little as 20K but you'd need a lot moolah for a full restoration and the mods you want.
My sincere advice - Find a good 5 speed MPFI 800 or an old zen and work on that car. Although i'm a lover of the SS80, it can be quite frustrating to work on and modify the car - especially on a budget. However, if you have all the money in the world and the time, a well kept SS80 is a joy.
Here's a picture of my car before I sold it in '04. Apart from window tint, sealed beam headlights, a Pioneer Stereo and a better aircon compressor, it was almost factory stock. It was amongst the first 100 to roll out in end '84.
I really really miss her so much 
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