my 1st gt4 ATA done this and i bought a new engine and dropped it in, big ends depending on how badly damaged they are could run into a decent or a hefty bill there is no cheap option as labour is where your going to get hit badly.
They will damage the crank badly leading to rod, piston and block failure. You may get off light depending how long its gone on for, the main reason for big ends going is poor maintainance or oil starvation. So give that car a good going over before spending big money on it as if some neglected something in one place they generally didn't care about the whole car. Hope its not that bad but thats the worst case scenario.