I just had the liner replaced by a guy I trust. We selected a design in 27 gauge thickness from Pegasus liners, which is a local company in New Jersey. My pool is 20x40 but otherwise looks almost exactly like yours. We had to make a rush job to be ready for the Princess's graduation party, so I paid a bit extra to expedite the manufacture in a few days instead of a few weeks. But it worked out well. Total cost all in was around $2800.

We pumped out the old water in about 3 hours, and then a team of three guys took the better part of the day to remove the old liner, patch the vermiculite base with fast-set material, then install the new liner.

Next, we turned on the hose and began to fill. It was taking so long, I hired a water company to truck in a load of water, which ran another $300. But again, I couldn't wait a week for the garden hose to dribble in 30,000+ gallons.

I did inquire as to the difference between 27 and 30 gauge thickness and my guy said it wasn't worth the cost differential. He installs about 50 liners each season, so I took his advice.