SCI/other credible journals for low budget authors
Many journals do not charge any publication fees at all.  For example, subscription journals often fall into this category, and in most fields there are plenty of subscription journals.  If all the journals you are finding charge fees, then I'd imagine you aren't searching broadly enough (although maybe publication fees are particularly common in your field).

Furthermore, journals that charge publication fees ought to give fee waivers to authors from developing countries.  Their web sites often explain the details, and if they don't you can write to them to ask before submission.  They might in principle say no, but it can't hurt to ask.