I like how yaksailor made his bait tank from a $13 5 gallon plastic gas can. Modeled somewhat like the Hobie design but far cheaper. Here is the link:
http://www.bigwatersedge.com/bwevb/s...ad.php?t=10529
I think the most expensive part would be the hatch ($43-$55) for that alone.
Hobie 6" Twist & Seal hatch:
http://www.austinkayak.com/products/...eal-Hatch.html
Hobie 8" Twist & Seal hatch:
http://www.austinkayak.com/products/...eal-Hatch.html
The cans come in Yellow (diesel), red (gas) & blue (Kerosene). Here is a link to Briggs & Stratton Gas cans:
http://www.theplasticsgroup.net/consprod_gasc_ul.htm
Just add a few other items (plumping and wiring) a battery & pump.