I’ve never had to file a tax return, but need to do so now to apply for a Green Card for my spouse

The Green Card application generally requires tax returns for the past 3 years from the sponsoring spouse.

What would it cost to have TFX file for me?

The cost of filing 3 years of tax returns for a client with low income and no non-wage income is $840 (3 returns at $350 each, minus a 20% discount for filing multiple years at once).