There is a couple of luggage storage service in Tokyo Station as well as coin lockers.
One of the largest cloakroom services is in the GRANSTA located on the basement floor of Tokyo station. However, it is only available from 7:30 a.m. to 8:30 p.m.
The other one is Rail Go Service operated by JR East and located outside of Yaesu South Exit. This is also for a daily use.
The link below might be helpful for you to find out more about cloak services in Tokyo station.
http://www.japan-guide.com/forum/quereadisplay.html?0+107000
As to coin lockers, the price differs depending on the size. (100 yen – 700 yen).
There are many coin lockers available; however, most of them are often occupied, so a cloakroom service may be a better choice to assure your storage.
There are also a lot of coin lockers in Shinjuku station as well, however, those lockers are also often occupied.