Google Books has access to many free eBooks on Romans. Click the links below to view. NOTE: Books available on Google Books are not always available in a full text format. Previews for most books are available.
To view more than is listed here, use the Google Book Search box and conduct a search for "Romans AND Bible commentaries."
Here are some other free eBook Bible Commentaries. Some of them will require you to download a pdf file.
Free and almost free resources available on the web.