Anyone know how much would be to run home watter + heat from LPG (propane) instead of city gas ?

we live in toronto downtown , and the gas company charges ridiculous $50/month in service fees on top of the 17cent / m3 (cubic meter), we seriously considering changing from city gas to LPG (bolted propane), the problem is that propane is sold in kg's and not m3 and i don't know the conversion, as well not sure if you need more from 1 or the other. any one has experience in how much would the monthly cost ? is it worth it ? $50 every month is a lot for us when out effective gas bill is only about $5-$10/month (its a home, not an apartment)