Move Website from Bigcommerce to Magento

Our website is currently hosted on bigcommerce and we would like to move to Magento platform. We feel like our options are limited on bigcommerce and are facing many issues.. We had previously hosted on magento and made the move to big commerce in 2019 because we were advised it would help to increase sales.. but we did not really see much difference.
Please contact us f you have experience with both platforms and advise how much is your proposed cost for this project?