I too was looking for the best solution to the ship basing problem and was not able to find metal bases in the needed sizes. I thought about trying to buy sheet metal and then cut it to shape but I can't find a store that sells suitable sheet metal, and I don't know how I would cut it adequately.
So I opted for plastic sheet. I went with a product that is readily available at all the chain hobby stores (you know the ones that don't carry miniatures) and railroading stores. It's by Evergreen Scale Models and I use 1mm thick plain sheet styrene (sells for $2.25 for two 6x12" sheets).
Then I needed a way to cut the plastic so that I would get an accurate cut each time and quickly. I found the perfect solution. I bought a floor tile cutter from Home Depot. It looks just like a one of those paper cutters you see in the office mailroom.
I also came up with standard base sizes for my ships. Since I can make them any size I want to I decided to make a different standard size for each class of ship as follows:
Ship Type Base Dimensions
CV, BB, BC 12.00 x 3.00 cm
BB (old), CA 9.50 x 2.50 cm
CL, Tanker 9.00 x 2.25 cm
DD 6.00 x 1.75 cm
FF 5.00 x 1.75 cm
SS 4.00 x 1.50 cm
Merchant Ships 7.00 x 2.25 cm
Now that I had all the ship bases and in the sizes I wanted at an economical price, I needed to make them look realistic - afterall, we put so much work into the bases for our land armies, I felt no different with needing the ships to also have beautiful bases. So I followed the instructions on GHQ's website for making ship bases and the finished product is below:

Top view

Side view
Hope that helps.
Chris