That’s a difficult one to answer. Range depends on a lot of things and not just how heavy the car is. The weight of the car has the biggest impact at low speeds however as you increase the speed the wind resistance becomes a big factor to the extent that once you’re up to cursing speed it will generally overtake any losses due to weight. So a light non aerodynamic car may have a lower range than a heavy sports car. Also it isn’t always the case that a smaller car is lighter, particularly with some of the older “more solid” small cars which can be heavier than you expect.
The other factor is what type of battery, I’m guessing you’re looking at lead acid but if you went with other more expensive types then weight isn’t as big a problem but price is.
As a general rule though a car that can carry more weight does have the potential for more range but will need a bigger engine, controller and other components so doubling the battery capacity will not double the range and would increase the price so your $ per km ratio would drop.
Personally I started with a small car and tried to configure it to do just the range I needed for day to day driving. This helped keep the costs down compared to what a heavier car with longer range would be. Once I’ve gotten this conversion down pat then I’m looking at doing a second larger car with higher range and performance, probably a sports job.