What sorta disc do you have, if it's a bolt on one, your need a 3 or 4mm allen key, or a t25 torq. if it's a centerlock one, your want a shimano freewheel tool. as in the one made by shimano, As it's deeper then other peoples ones, and will reach. or a e type bb tool, depending on the lock ring, holding it on.
Changing the spoke it's self is easy enough, once the disc is off, just make sure you weave it through the spokes in the same way the others are, and take your time doing it up. If you do a little at a time, and when it gets tight, dont do more then one turn. As it starts to affect how true the wheel is, alot then.
Your need a spoke tool, and possibly a bladed spoke holder, if it's a flat spoke.
As your willing to pay for it to be done, you maybe better of taking it to a shop, and getting them to do it. It dosn't tend to cost too much for a spoke replacement.
Shimano cassette tool.
http://www.chainreactioncycles.com/shim ... -prod23751
