hello dear
u want CNG beetle bro it would be cost around 80,000 to 100,000 (everything is perfect) without cng and normal condition around 50,000 to 60,000 in Lahore (i do't know about karachi prices)
and 2nd question about heating prob or burn out etc.
so bro i m using beetle since 1995 i never faced these prob. in JULY 2004 i travelled on CNG beetle from Lahore to Peshawar whithout any prblem etc.
and 3rd question about maint. etc.
yes maint. of beetle is bit expensive if u compare suzuki etc.