I'm filling in my own pool. You can have a company bring in fill dirt. The problem is that while the dirt (or rock) is relatively cheap, the trucks and the cost of the drivers is not. I was looking at $150 per truckload (10 cubic yards) plus the cost of the dirt. You can imagine how fast that adds up. You can get free dirt (if a construction site) is doing excavating and needs to get dirt off the lot. But you should discuss with the company where they are going to put the dirt (and probably put boards or something) down to prevent them from sinking into the lawn. Then there is the issue of how to get the dirt into the pool. This will usually require heavy equipment (bobcat/backhoe, etc.). This stuff can cost $200 a day to rent.
This is a fairly complex project and it can cost several thousand dollars. Good luck.