Thrusters and fish are fine, it's just that your mistakes will show more in the ride of the board, but it doesen't really matter that much, and there's just more things that can go wrong (breaking off tips on the nose and tail, especally with a fish, and it's harder to get the crack of the fish right(especally on the steve lis types, the actual fish))
I know what you're talking about with the shipping, try to go find a big local shaper and see if you can either try to buy some blanks off him, or hitch an order with him. Or, you can try using EPS (expanded poly styrene; styrofoam) foam and get a blank from home depot, or Sfoam.
Sfoam is like clark, they cut their own blanks out of EPS foam and glue in stringers for you, so you can get blanks either cut to a surfboard looking blank shape or just a big rectangle with rocker. You can also get them stringerless, and lots of other stuff.
I have actually only used EPS, I haven't used Sfoam because of shipping also, but go to home depot, buy some foam, and glue up my own blanks. I'm currently doing a project with my dad to try and make my own urethane blanks, but actually making any will be a long ways off.
Do you want some general dimensions for a fish or sb?
the sfoam blank catalog isn't quite as hard to choose from as the clark because it's an even density the whole way though, so you don't need to worry about getting one close to finished dimensions, just the more foam you get the more it will cost, and the more you'll have to take off. here's the site,
http://www.sfoam.com/ you can take a look and decide if you want to use it yourself.
But with EPS, you gotta use epoxy, or else you'll melt your blank. I highly recomend Resin Research epoxy, it's the best stuff. Their site is
http://www.resinresearch.net/
if yous till have anymore questions, ask away