It's not as hard as you might think. I have leveled both of my pools (18' and the new 24') by hand using a roto-tiller and a shovel. It's a lot of work, but the process is simple:
1. Remove all of the sod. ALL OF IT.
2. Find the lowest spot in the pool area. To mark out the pool rough dimension, simply drive a piece of rebar where you would like the center of the pool to be. Make sure the top of the stake is higher than the highest point in the pool dimension by several inches. Tie a string to the top of the stake. Pull the string taught to the furthest dimension of the pool and use a line level to level it. Keeping the line taught and roughly level, walk around the center stake and spray paint a line at the end of the string. Now you can find the lowest spot in the dimension.
3. Since I don't know the dimensions of your pool, I will use my 24' as an example. Take a 14' 2x4 (very straight) and lay it on it's edge the the 1.5" side facing up. About 4" from one end, drill a hole into the narrow edge slightly larger than the diameter of the rebar stake you have in the center of the pool, and about 1.5" deep.
4. Place the 2x4 on the rebar using the hole you drilled.
5. Rotate the 2x4 around the pool perimeter so the end is over the lowest spot.
6. Place a 4' level on the 2x4 and hold the 2x4 level.
7. Have an assistant screw another 2x4 vertically on the end of the level 2x4 so that it creates a "leg" of sorts with one end on the ground.
You should now have a long 2x4 sitting on a piece of rebar (in the hole you drilled) with the other end supported by another 2x4. Like this:
I used an old mobile home truss, but the idea is the same.
8. From the lowest point, measure from the ground to the top of the horizontal 2x4. Remember that number. I actually turned my shovel upside down and put a mark on the handle as a permanent reference.
9. Start digging around the perimeter, moving the 2x4 around with you as you go. Check with a 4' level often. When all points around the perimeter are dug down to level, start at the low side again and dig a path toward the center stake, using the measurement you obtained earlier to check the depth as you go.
10. Simply continue around the pool area until all points match the first measurement.
11. Your pool base is level.
It's hard to tell from the pic, but I dug down nearly 15" on my high side. In the background you can see the dirt starting to pile up. It's a lot of dirt. I use it to fill low spots and such. Save the topsoil for raised bed gardens.
Questions? Ask away. I have lots of pics.