It depends on the type of edition of specific manga.
Small, mainstream manga, like Shonen Jump (VIZ), Kodansha, Yen, Dark Horse, Seven Seas, all publish paperback manga. Quality varies among them, some, like Shonen Jump, is only black and white-even the colored pages. Yen has a few single colored pages, and certain Kodansha titles have no colored pages but have a single colored cover page. With all these factors, the price (and quality) can range from 9.99-13.00 USD.
The editions with the best bang for your buck are omnibus editions. They tend to be 2-3 volumes for the price of one, usually 15.00-20.00 USD. My problem with these editions is quality, and it depends on the publisher: for some, paper quality and cover is so cheap, much more so than single volumes. Some have all color pages-colored, extras-such as interviews and additional stories, and a flap. Unfortunately they don't include the cover art of single volumes, so if you're a collector like me, it is very disappointing. Finally, some omnibus are of great quality but the cover is paperback, so sometimes it gets uncomfortable holding the book, and turning pages can be complicated. This is where hardcover comes.
A few publishers have hardcover manga that can range from 15.00-20.00 USD. Paper quality is good too, not the best but still better than paperpack paper. Unfortunately, a few tend to be single volume, which in my opinion is too much for a single book. Don't get me wrong, it looks nice but it will definitely put a hole in your wallet.
Where hardcover really shines is in the specialty department. Collector editions, omnibus, and bi/tri-annual release, are the best option and worth the price.
Of the hardcover editions I have are: "Bleach" Volume 1 Collector edition, "Vinland Saga", and "JoJos' Bizarre Adventure". They have great paper quality, a couple or multiple colored pages, and "Vinland Saga" and "Jojo..." are omnibus-2 volumes for the price of one. Best of all, these were a one time release or slow release so I can save money and purchase them.
I think the "JoJo" release is the best: a hardcover with new original art by Hirohiko Araki, colored pages, good paper quality, extras, and 2 volumes per book.
Bottom line: if you want multiple titles at an affordable price, buy paperback. If you want a memorable product and is special to you, with a specific signature; buy hardcover.