I'm currently low income, & need a wisdom tooth extraction. i was told that i need a bone graft to avoid bone loss in the future. is there a window of time i can take between extraction and a bone graft, or are both at once necessary?

Unless the extraction is a bony impaction that will require the removal of bone to access the tooth and the procedure would compromise the distal support of your 2nd molar, a bone graft is probably not necessary. You will not be placing an implant at that site.

Necessity for treatment and staging of treatment are decisions to be made between you and your treating Dentist. As you are talking 3rd molar surgery, I trust that you are seeing a specialist Oral Surgeon. If you have questions, seek a second opinion. But an examination is required to be able to answer your question. Make sure to take your x-rays with you.

Bone grafts with wisdom tooth extraction are rarely needed…only in special cases. Get a second opinion

You don't need a bone graft unless the tooth in front of the wisdom tooth to be extracted is missing and the tooth in front of it also, and you plan to get an implant bridge. Since you possibly can't afford a bridge leave the area as is after the extraction. See if you can get on Medicaid to help cover the cost of the extraction.