I say go for making your own!! There is nothing like setting on your own handy-work. It's not hard to do if you have or have access to a table saw and drill press. I've done it totally with hand tools just to see what they went through in the "old days". Not any harder, just takes a little longer. OK, a little bit longer than a little longer.
Ash is the most common wood used but I've used cherry, apple, mahogany, sitka spruce, Fir (Not that good...over time you can get splinters in your butt), Maple and walnut. But if you can get White Ash I would think that is the best.
As Max says, use mortise and tenon joinery, it's about the strongest going. Pretty much fool proof if you follow the directions given in any good woodworking book and measure carefully.
Of the books mentioned above, I think Gilpatrick has the clearest material on making seats. I bought it just for that section and found there was a wealth of other information that was useful. His emphasis is on strip built canoes but he has insights that apply to many other styles of building. They are easy to find (ebay has lots) and inexpensive to boot. And if you want to contact him, he's very friendly and helpful.
The other book that has a fantastic section on seat building and caning is John D. Michne's, Building an Adirondack Guideboat. Very well done book.
Caning is easy once the holes are drilled. But if you set up a little jig with your drill press the drilling doesn't take long either. I find caning by hand quite therapeutic so don't mind at all.
With a few simple jigs it takes me about two hours (with a couple coffee breaks) to make up and glue a set of two seat frames. The varnish actually takes longer due to drying time than anything. I usually spread the caning over a couple evenings while watching TV. So, I figure at my pace, about a week from rough board to installation into canoe. I usually let them sit a little longer to let the varnish harden but you wouldn't have to. I don't think you could get them delivered from Old Town in that length of time...maybe, depends where you live. And then you wouldn't have the pride in doing it yourself if you purchased them.
But before running out to buy any books follow Max's point and check your local public library. You'll be surprised what the have.