With enough money you can convert any car to electric, but that doesn't mean you should convert any car to electric. The easiest cars to convert to electric are cars made before 2000, and are manual transmission.
Unlike in an internal combustion engine vehicle where the motor is what makes all the power, in an electric vehicle it's the battery through the motor that makes the power. So choosing the right motor will be determined by the system voltage, vehicle size, vehicle weight, and drivetrain.
The traction battery of an electric vehicle is it's most important part. There are a lot of options for batteries, but this is likely where you'll spend the most of your money. The industry standard currently are Lithium ion batteries, but many enthuhsiasts use LiFePO4, or CALB batteries.
In your electric vehicle conversion you'll have two different electric systems. The high voltage system (battery, charger, and motor connections) and a low voltage system which runs nearly everything in your car from the AC system to the headlights.
At nearly any voltage electricity is dangerous, and it should be understood that without proper precautions these projects can be harmful and dangerous. Consult a professional if you have questions about any step of the process.