You would think that all the quotes you received should be around the same price if the are quoting on the same project but there are lots of reasons why they are not. Some companies offer different customer service then others, some are cleaner, some get the job done faster and these are all good reasons to charge more. Some of the companies that seem way cheaper then the competition are not following the rules. Anyone you hire needs to have insurance, WSIB coverage for employees (and sometimes the boss and sub-trades), licenses for electricians and plumbers, file their taxes and all this costs money. They also need to follow minimum code whether you require a permit or not. A lot of these companies not only do not guarantee their work but may not be around 6 months from now to fix it if they do. Ask for references, testimonials or pictures of past work. If they are cheap, only accept cash and don't give you a bill then you have no way to go back on them if you get damage to your home from their work.
It takes a lot of work and knowledge to do most renovation project properly so don't put the price first. If you do you will get what you pay for.