My dash cluster has stopped working. My brother in law tried to re-wet the solder. So it'* been tampered with and not re-buildable? What'* the cheapest most effective way to replace it?

Junkyard. Find one from the same year, model. Go home rip your dash apart to the point that the cluster is ready to come out. Go to dealer, with 'new' cluster in hand. Have them transfer mileage to new cluster. They need the old one installed to verify mileage. They will probably charge you at least 1 hour shop labor rate to do this.