I visited today Hascol pump on Shara-e-faisal to get the details of LPG, current price of lpg is Rs 56/liter and it will go up in winter upto Rs 75. Sales person there has experience of conversion mostly on corollas and he says that 1 liter Lpg gives around 8-10kms with ac in Karachi city.
He quoted me conversion cost of 38k for 50 liters tank in Wagon R. There was another guy with 88 charade filling at station, he also told me his car gives 10 km/l.
If Wagon R also does 10km then per liter fuel cost will be Rs 5.6 in summers and Rs 7.5 in winters, plus you have to keep the petrol to start the car which will be Rs 500 per month, Fixed cost of conversion is Rs.38k
Filling is no issue, it can be filled from any LPG filling station where rickshaw wallas go.
Cost of running 1500 km per month, with LPG
1500/10 = 150 * 56 = Rs 8400/ month
1500/10 = 150 * 75 = Rs 11250/month
Petrol Cost 500 * 12 = Rs. 6000
Total annual cost variable [summer months(8)+ winters month (4)] = 8400 * 8 + 11250 *4 = 1122200 + 6000 = Rs. 118200/anum
Total Fixed + Variable = 118200 + 38000 = Rs. 156200/anum + fitting
With Petrol, 15 km/l avg
1500/15 = 100 * 106.9 = Rs. 10690/month
Total Annual cost = 10690 * 12 = Rs. 128280/anum
Diff = 1562000 - 128280 = Rs. 27920
Saving of around Rs 10000/anum doesn't worth it, it means I will recover amount of conversion by 4th year. We should also consider void warranty, no trunk space.