If you are doing multiple returns, it may be cheaper to use TurboTax CD/Download (for Windows). You would be paying for a number of returns upfront, but the returns are discounted compared to the TurboTax Online returns. There is even a 20 return version of the software, which comes out to about $8 per return (before tax).
If you want to use TurboTax Online, some retail partners like Costco or Walmart sell multi-return packages of Deluxe and Premier. Please be aware that the price per return of TurboTax Online is based on what you enter in your return. So, if you do get a multi-return package, some returns still might require you to pay to upgrade the return.
Please note that the Canada Revenue Agency (CRA) limits the number of returns that you can file online through NETFILE to 20 returns.