Legit. volunteering organisations

I'm looking at volunteering in Ghana this year. I'm a volunteering virgin so I've no clue what the process involves.
I've been scouring the net for months and I have no idea what is a good/bad organisation.

I assumed I'd sign up with a group, get myself to Ghana and I'd crack on with whatever 'tasks' they threw at me. Never assume.
I had no idea volunteers could live it up in 4* hotels. Surely that is a holiday?
I actually want to be useful. I can holiday anytime.

Also, the organisations have fees? Obvioulsy, I don't mind paying if the money is going to the cause and my keep. The fees seem to vary so much from one group to the next.
What would you say is a reasonable amount to pay and what should I be paying for?

All suggestions and advice welcomed with open arms.

x x x x x

A mate of mine worked for

A mate of mine worked for these guys... they seem pretty legit...