What you are talking about is essentially a radio mike with a headset. There are issues about radio mikes and I don't know where you are which may impact on that.

Shure and Sennheiser do a number of quality mikes which fit the bill but you pay for what you get. GOOGLE will find you any number of deals.

The biggest problem with using them is that (unless you switch them off) you are always connected so if you mumble to your guitarist "have you seen that etc stc..." the audience will also hear it.

Dependent on your performance there can be advantages in being tied to a mike stand whilst singing or playing (it doesn't seem to inhibit Bellowhead).

Steve