Hi,
I’ve used Lit extension a few times and highly recommend their service. I’ve used them to migrate from Magento 1.9 to Shopify, and more recently to migrate back from Shopify to Magento 2, all with great success. They can also custom code for things like importing into extensions, or only exporting active accounts etc, which is often worthwhile when migrating to get rid of the dead accounts.
Your cost is based on entities, and is the highest amount, os if you have 2000 customers and 10,000 orders, you will need to pay for 10,000 to get the info across.
Ask for a discount on their sales page (their chat support is great) and they usually offer 5 or 10% there and then
Hope the above helps