Litter pans are a problem. Especially when you have a large cat who can't fit in a small litter box and a dog who considers cat poop a delicacy. It's been a struggle to find a commercial litter box the cat can enter and the dog can't.
On average, the cost to have an above ground pool deck professionally installed can range anywhere from $2,500 to as much as $8,000. The costs really come down to the type of material being used, the size of the pool, the design and contractor building the deck.
If cost is an issue, you might want to consider a below ground pool with a liner rather than a gunite pool. Add a spa, decking, and high end equipment and you can easily be up in the $40,000 to $50,000 range, depending on size. Talk to a few pool owners and pool builders in your area for more detailed information.