This cost me 30 dollars in wood and some extra for tools. So this will save you about $270 in new board costs.
Warning: This board is not for beginners, it is not very buoyant and does not have a fin (although one can be added.)
Step 1: Acquire Accoutrements
Screwdriver (electric) and screws 2.5"
Waterproof wood glue
Newspaper (to keep work area clean)
Sealer (eco: linseed oil, ease: varnish)
Wood for surfboard and frame clamps:
5 or 6 1"x4"x8'
The 5 1x4's are what you will be making your board out of. I used pine but anything that you find in your lumber (fir, cedar, redwood) store is probably fine as long as its not too heavy. The 2x4's and the short 1x4 will be used to make your frame clamps. They can be of any wood.
Step 2: Build Frame Clamps
This is supposed to cost as little money as possible so I decided to build clamps instead of putting out for $30 clamps. These clamps will hold the planks together while the glue dries and keep them all flat.
I used 5 1x4's so my board will end up being about 18 inches wide. If you use 6 it will be closer to 21.5 inches and will will need to make your frames wider.
Cut your 2x4's into eight 24" pieces and your short 1x4 into eight 2.5" pieces.
At this point lay four 2x4 pieces down parallel 2 feet apart and lay your surfboard planks on top of them. This ensures you leave enough space to squeeze your shims in when the rig is all together. Put the 2.5 in pieces outside the planks on the 2x4's that should be sticking out the sides of the planks. Now sandwich the planks with the remaining four 2x4s. Hold in place and put one screw through each 2x4 into the 1x4 below. The screw should not go through the bottom 2x4, if it does back it out a little and it will be fine.
Step 3: Glue and Clamp Planks
Put the top half of the clamp (the one with the 1x4 screwed onto it) on the bottom and place the four other 2x4's to the side. This makes it easier to screw the clamp together.
Now put the planks in the bottom clamps making sure they are aligned at the top and bottom and push them together. Place the free 2x4's on top and screw them into the 1x4 blocks.
Time to shim it tight! I bought regular door shims but they were too thick so I had to split them in half and they worked great. Using three shims for each clamp hammer them tight. You only need to do one side.
Wait for it to dry for at least 24 hours.
Step 4: Give Her Some Curves
Be creative it's your board, do whatever you want.
Once you have the shape you have to plane it flat, sand it and round the edges.
Step 5: Waterproofing
If you use linseed oil you will have to put on several coats and will have to re-add it every so often to maintain the finish.
You can also use varnish which will require less maintenance.
Linseed oil is more eco friendly but varnish is easier. Its up to you.
Step 6: Optional
Hope this instructable was helpful and you will be surfing in the style of ancient Hawiian's soon!