In general, If you are attaching an affidavit, it must be notarized. Cost-saving at this stage may result in undue costs and delays later on in the process. You must contact an immigration attorney to get specific advice in regards to your situation.
I understand everyone wants everything for free nowadays. Please comply with the requirements regardless of how much it costs or it will cost you more. Consult a lawyer to make sure.
This answer is not intended to replace a consultation with an attorney and does not create an attorney-client relationship.
Yes, personal affidavits should be notarized, however, you do not need to submit any such personal statements with an Form I-130 petition.
Kindly be advised that the answer above is only general in nature cannot be construed as legal advice, given that not enough facts are known. It is your responsibility to retain a lawyer to analyze the facts specific to your particular situation in order to give you specific advice. Specific answers will require cognizance of all pertinent facts about your case. Any answers offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship.
If you want to do it right and have better chances to get visa then you should. Also seek attorney's advise on all the paperwork you are filing. Plenty of good attorneys on this forum. Good luck
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