Dear Mazin, 

Some journals have a lower fee for medical doctors, if you are not a MD you have to pay more:

Scandinavian Journal of Primary Health Care: online manuscript processing

Scandinavian Journal of Primary Health Care is an open access journal providing free access to research in primary health care. Current publication fees (as of 1st November 2013)

• Members: EUR 400

• Non-members: EUR 1,200 

There are about 43000 journals that are listed in pubmed:

ftp://ftp.ncbi.nih.gov/pubmed/J_Entrez.txt

You have to choose the most appropriate one that falls within the domain of your research.

Except open access journals (which is a recent concept), all journals wouldn't charge the authors for publishing their paper. In most cases, publishing in journals with impact factor is difficult than the journals with no impact factor, yet listed in pubmed. Higher the impact factor, more difficult to publish articles. Selecting the most appropriate journal would help in getting the work published quickly. Otherwise, articles would get rejected if the editors/reviewers feels that it is not suitable for publication in the journal. 

The fact that most of the publishers rely on making money by selling articles, they would require a small fee to download individual articles. That said, these articles can be downloaded at PMC websites (http://www.ncbi.nih.gov/PMC/ instead of http://www.pubmed.org).

There are numerous predatory journals. Until otherwise, you're not sure, you might end up publishing in a journal which has no merit. It might be available in journal website, however, it might not be available in pubmed / ISI listing.

Finally, since people can post their papers in RG, there is no legitimate concern for your question. 

ftp://ftp.ncbi.nih.gov/pubmed/J_Entrez.txt