Whoops, this thread slipped under my radar for a few days there.
I'm not the best person to answer this question, since I greatly prefer to read manga in Japanese these days, but a quick search yielded the following as some sites where you can legally read manga, at least some of it for free:
・ComiXology and ComiXology Unlimited
・MANGA Plus by SHUEISHA
Keep in mind I haven't really looked through these sites, for the most part. If it's a publisher, like VIZ, then the amount you can read for free is probably extremely limited (they are trying to make money, after all), but they might have something like a series where they keep only the latest chapter up for free of something being simultaneously published at the same time as in Japan. But Crunchyroll does seem to have a selection of titles that can be read in their entirety for free.
I'd also strongly recommend checking out your local used bookstores! At Half Price Books, the price for a used volume of manga is usually only a few dollars, and I think sometimes as low as $1. Way better than paying $10 for a new volume! The selection at any given store will be limited to whatever they happen to have, BUT nowadays you can go online and shop Half Price Books for any book they have at any Half Price Books store nationwide, and they will ship it to you.
Let others believe in the God who brings men to trial and judges them. I shall cling to the God who resurrects the dead.
-St. Nikolai VelimirovichMAL