my bro, cng kits are rather very hard to find new ones and the used ones are a bit tricky. No idea about prices, sorry.
But going for cng in an auto, emm, never ever recommended.
Esp for civic, Prosmatec + CNG= Pathetic.
better get a manual tranny and then get it cnged
also a new or may be a less used kit is gonna cost u something above 65k, which u won't be able to save with avg savings of rs 1.5 or 2 per km in cng. The car will also become vulnerable to different mechanical problems as well.