That's a relatively small pond. If you had the patience, you could empty most of it onto your lawn with a 5 gallon bucket, then pull up the liner and let the rest drain into the soil.
Personally, I would not use the rocks to fill it. I have a lawn that's so full of rocks it's impossible to dig anywhere. I would fill the bottom 6-8" with whatever cheap fill you can get locally and then 4-6" of good topsoil. You should need slightly less than a full-size pickup load of fill, probably $15-20 at your local gravel pit if you load it yourself.
You could rake 1" of compost over the top to help the lawn seed get established.
Some issues that you may have with rocks:
- If you live in an area where it freezes in the winter, the rocks will heave and make the lawn uneven.
- Even without frost heaves, over time the soil will settle into cracks in the rocks and you'll have a lumpy area of lawn.
- Over time you may forget what was in that spot and rediscover that it's full of rocks when you want to plant something there.
Keep in mind that even if you fill as I've suggested, you may have some settling occur over time as the soil in that spot compacts. Overfilling/mounding up the area may help with this, but it's hard to know how much to overfill in advance -- you may end up with a permanent mound there if it doesn't settle as much as you expected.
If you do decide to use the rocks for bulk as you fill it, I'd suggest watering in whatever you use for soil so that you have fewer issues with settling.