If your Dad is a novice, then he will be VERY glad he bought a used O/U. Not to knock the Lanber and the price, but consider this;
$900 will get you a new Beretta White Wing. Stress NEW. Uses tubes, 3" chamber, good all around gun. I have one. Add some Pattern Master choke tubes and you have something. Not so pretty that you might mind taking it in the field and getting some scratches on it, but good enough to kick some supposed experts asses on the skeet pad.
$700 to $900 will get you a used Ruger, Remington, Winchester, Browning, Beretta and others. Field grade or Skeet guns.
The cheapest used guns will have fixed chokes and 2 3/4" chambers. But in many cases these will be top of the line guns from their day, and all he will need. Dedicated Skeet guns, but more gun in terms of shooting skeet, than any new gun for the same price.
If you look hard at used, dedicated skeet guns, you will find a lot of used guns in the 600 to 800 range. Zero in on the model that fits him best first, then shop for a deal on it. Also compare the Lanber to the Whitewing.
The other issue is this, if he spends $500 on a Lanber now, he can always sell it for $350 to $400 later. If he spends more now, he will probably keep the gun he bought, thus saving money in the long run and will have a better gun. BUT if that cheap gun fits him wrong, he will suck at Skeet and own a gun he hates.
Have fun spending his money!