The cost of GED tests is determined by local testing centers, so you will have to contact the center for more on the same. On the average, though, most testing centers charge around $150 for the entire test. Some centers will, however, charge a higher or lower amount.
Call your local community college and ask them. $150.00 sounds like a lot to me. I think it should be free...course, free is normally a thing of the past. Your local library has GED Workbooks to help you prepare for the exam. The test is not that hard. So proud of you doing this! Way to go!! Yay!