Once you excavate, you install the walls, the plumbing and electric and then we (when I say we I mean DH and his friends

) spread a concrete and vermiculite mix on the bottom before placing the liner in. We bought bags of both and rented a mixer to mix it ourselves.
We did hire a concrete truck to come deliver concrete to pour in behind the walls once they were up and under the steps. Then we hired a concrete guy to do the surrounding patio. This was the most expensive part.
The kits come with a video and the folks we bought from were very available by phone with questions. It is no small project, however. We could have done it cheper but we really wanted the l-shaped pool (rectangular was less) and we got a salt water system. We have quite a bit of patio around the outside too, which adds to the price. A pool of that size and shape would have been 35 grand to have someone else install.