I'm not sure how many of you saw this thread because it was in the kayaking gear forum, but it's certainly worth a nod here. Linked below.
I went ahead and took a stab at making my own pump today, and I have to say I'm quite pleased. A few hours of work and about $40.00 in parts and I have a new $200.00 quality pump. Here is how it turned out. Needless to say I'm super happy with it.