Give this calculator a try with the information specific to your home and costs of energy: http://www.propanecouncil.org/calculator/
Of course this will only help you calculate the cost to heat your home comparing between propane and electric. You still must figure for the initial installation costs to convert your existing system from propane to electric.
Assuming you have a gas fired hot air system with ductwork already installed, you would need to replace the exisitng unit with a new electric furnace or heat pump, and retain the duxtwork system. This may also cause you to to replace your electric service, because of the large amonunt of electric power the electric heat unit will need.
Just to throw some wild numbers around, if the service costs $1500.00 and the new electric furnace costs $5000.00 complete with installation, total conversion will cost $6500.00. Now to realize a payback in a reasonable time, say 5 years, you would need to save at least $1300.00 per year to begin saving money in the sixth year by converting from LP to electric.
I am sure there are other misc factors that will come into the equation, but with this information I believe is enough to get you thinking of the result.