You can trace the database included, searching by the keyword "Signal processing" to find the journal and its corresponding ISI (IF). Most of them are free.
As I know, almost all Elsiver journals of Q1, like Neuroimage, are free of charge,
Pattren Reconition Letters and Pattern Recognition are free too.
IEEE journals of Transactions level, like IEEE TIP are free, "Journal" level and "Magazine" are partially free. For example, IEEE JSTARS takes 200USD fee for the pages over 6 page limit.
Almost non-open access journals are totally free, you just search on Springer, Elsevier, Taylor&Francis, etc. Some open access journals also can be free, they are always of academies, universities.
Almost all journals published by Elsevier and Springer are free if you chose to transfer the copyright to them and your research will not be open access which limits the citation.