Load Range G tires are heavy-duty ST-series (Special Trailer) and designed to carry heavier loads. As a result, they are not inexpensive. Don’t be tempted to substitute less expensive LT-series (Light Truck) tires that might be available in the same size. They won’t adequately support the load imposed by your 5th wheel.
You may find a dealer that will shave the price a little, but in general, ST-series tires in the size you need are going to be around the $275-350 price point unless you go with Chinese-made off-brand tires and I would not recommend that.
Good luck.
TJ