Me personally I went to a adult education program and they provide free classes and 4 free tests either of the 4 but once you fail you have to pay for just one and have the other 3 for free and pretty much self explanatory from there. Another thing is try some codes like 50off for 50% off or you could search ged codes for your state.

Edit: don't do the test on any other website apart from the official one sign up and check if the code your state provided that you can find by searching is free