Bus or Train to Osaka from Tokyo

We will be going to Osaka after 5 days in Tokyo. What is the most economical option to travel to Osaka from Tokyo so that we will be on time to check-in at the Osaka hotel at 3.00pm.
Bullet train is expensive, bus is cheaper but slower.

How to travel by bus to Osaka from Tokyo?

Thanks.

The overnight bus is most economical. All the options are outlined on the below linked page:
http://www.japan-guide.com/e/e4006.html

You could also consider flying - Peach is a budget airline operating in Japan that I used to fly from Tokyo to Osaka. With luggage, the price was around AUD$79 (from memory). The flight itself is much faster than a train or bus, but bear in mind you must get to and from the airports and also be at the airport well before departure time, unlike buses or trains where you can arrive shortly before departure.