It really depends which Java skills you are looking for and for which platform the solution will run on. If this for a web project then which application server, database, middleware technologies is it using? Getting a developer with the right mix of skills for your project can be hard and this is when it starts to get expensive.
As a rough guide if you're looking for a good Java web developer in the UK to work on an existing project then allow £400+ a day. On the other hand if this is a new project and you need a good Java systems architect then you can easily pay £1000+ a day.
The Java programming language itself is easy to learn but it takes a lot of experience to know how to use it to write robust commercial applications so experience is very important.