A certified translation for USCIS needs exactly two things: a complete English translation of every foreign-language document, and a signed certification from the translator that it's complete and accurate and that they're competent to translate from that language into English. No stamp, no seal, no notary. It's one of the few federal requirements that would fit on a sticky note.
VisaDocTranslation builds every US order around that rule, at $20.39 per page with next-working-day delivery, or $40.08 per page if you need it within 8 hours. The same certified translation works for most other US uses too: universities, employers and agencies that ask for a certified English translation. If one of them insists on notarization, you can add it at checkout for $26.45 per document.