A 3ft will last your beardie around 5-6 months. Then the minimum is 4ftx2ft. It doesn't state the width in the auction - do you know how wide it is?
The general rule is that it must be able to turn around without it's tail bending ie touching the sides.

That is a reasonable price - seen as it does come with some equipment.

To be on the safe side, I would buy a new UV. These need replacing every 6 months anyway, and UV is so incredibly important to babies that it just isn't worth risking when buying second hand.

If it was me, I would also sterilize the wood - bake it in the oven for a while. This will kill of anything that might be on there (Beardies can carry mites, and that's the last thing you want)