We are setting up a new barndance / ceilidh band and I need some advice about equipment. We want to keep our prices down to start with, so I want to use what I've got as much as possible, not set up a sound system that would fill the Albert Hall.

I have 2 Coomber boxes that play tapes, they each have 2 microphone and one aux sockets. One is 65Wmpo 30Wrms and claims to be suitable for area of 1 badminton court. The other is 160Wmpo 75Wrms, suitable for 2 badminton courts. They can be linked together.
There is a separate volume knob for tape and input, also bass/treble controls for each, but no way of balancing the different inputs.

We went out last week, I plugged my radio mike into one box, the two other mikes into the other box, and balancing the 4 players was a matter of moving their chairs nearer or further from the 2 mikes! (It was a small room, we hardly needed amplification)

I think we should do better than that so I'm planning to buy 2 more mikes and stands, and a cheap mixer. What should I look for? I don't want to spend a fortune, but I don't want to waste money on something unsuitable. One of the mikes (a Coomber) I've got is very noisy if you hold it or switch it on and off. How can I avoid this?
How much will it cost me (UK)

I've got Bernard's advice on setting up a sound system just need a sound system now.