Newfound Woodworks sells the foam for a very reasonable price, and they have excellent customer service. You need to get the 3", and they will sell you a 3"x24"x27" piece for $28. This will be enough for a seat and some hip braces and proabably a knee knob as well. They also sell backbands. Get the Kajak Sport deluxe band. It's very comfortable, and easy to install. Also the back straps velcro so it can come out to reach gear behind the seat, but the velcro is huge, so there's no way it will come out without intent.

Don't worry if you don't have a grinder to sculpt with. I used a hacksaw blade that I bent into a curve and used it to scrape it out with, and used 80-grit sandpaper to sand it out the way I wanted. You can use a serrated knife to take out big chunks in the butt section to save all that sanding. There is some stuff on the market called sharkskins that is basically piece of metal with holes like on the fine side of a kitchen grater, but smaller and finer. It's supposed to give a much more smooth finish. I didn't try it but folks I know that shape surfboards have used it for that and say it works well.

Also while on the subject, there have been a lot of posts about people with "numbbuttitis" lately. It appears to be spreading. Here is my cure: when shaping your seat... the kayak seat, that is... don't do the "Farmall" shape with the ridge in the middle. Instead start with that shape, but then dig out about a 2" by 2" depression down the middle from the front to the back. There is a blood vessel that runs down thataway which does not like to be squished. That's why God made us with two humps to elevate that area and keep it from getting squished, not to mention other things that don't like to be squished, but I won't go into that. Once you try it you will see the difference right away. The seat may end up a little funny looking, but will be the most comfortable seat you ever sat in.

Oh, and when you get the shape roughed out, sit in it and think "where do I feel the most pressure." That's where you need to shave a little more off. You will see what I mean when you do it. The high spots will be where you are feeling the most pressure. Once you get it down to the right spot the pressure will be even all over your gluteus maximus. Don't worry about cutting off any excess. Just cut off whatever it takes to make it fit in the boat... the rest will displace water in the cockpit during a wet exit and that's a few less pumps of the bilge pump. Also it's added floatation. That's another reason I like foam bulkheads... even if the bow and stern are holed the bulkhead will displace a good 10 lbs of water by itself.

Good luck!

-Malcolm