It depends on how famous they are and by the type of contract they have.
The average Mangaka (not the famous ones like the makers of Bleach or Naruto) looks at roughly 8-10 hours a day, sometimes more, sometimes less. Generally, they have a 20-40 page submission to fulfill every month so you're looking at one completed page every day. This is not including the time it takes to write the story, and if the editor doesn't like it, you hae to re-do it (including extra art like cover art or graphic books).
You don't get an hourly rate, but a contract based partially on sales. An average contract usually for a beginner is $500 (per 20 page's + 10-15% royalties) from Tankobon volumes. Remember, volumes in Japan are about $5 unlike in the US (around $10-13) so royalties are really small which assuming it takes 5 hours per page (about 5$ per hour) and that If you don't hire an assistant. If you do, then the cut comes out of your salary and you do pay them an hourly rate; not a by contract.
This is why the majority of regular Mangaka's have a second job because being a Mangaka in the first place doesn't pay the bills. It's only if the Mangaka gets famous that they have a decent pay rate like Bleach which is about $120/page and Kubo makes 20 pages a week. He still has to pay for his assistants too.
If the series becomes an anime then they get about $660 per episode. So if it's a standard 1 color anime then they get a little under $8,000. They do not get royalties from DVD/BD sales--only that upfront episode price. The royalties from the DVD/BD are given to the sponsors and the publishing company and the animation studio. Most Mangaka don't even have a say in the anime's production. The publishing company handles it as the anime is only made to make money for the sponsors and to promote the original series. The Mangaka is busy working on the original series and since the publishing company wants to make money by being a sponsor and make money from their Mangaka's work - they have the largest say in how the anime is made.