Champagne tastes on not even a beer budget

Well, I've almost completed 3 repeats of the Backyard Leaves scarf, and I'm already thinking to my next massive project. For a while, like since last fall, I've been wanting to try my hand at designing something. I saw a great coat/jacket, and wanted to find a pattern; but alas, there was none to be found. So, being the crafty person I am, I decided to make it. Or at least attempt it. I got as far as a swatch, and realized there were other things that needed to be done in order to properly work this out. I tried submitting it to a book, and it was rejected (but it was nicely rejected). What I'm thinking is this: if I make it, go ahead and work up a pattern and make a sample, perhaps it would further my ideas and possibly open a door for other patterns to be published. Here's my dilemma...and where the title comes from. I need a bulky weight yarn, since it's to be a jacket/coat and having long pieces knit up quickly would be helpful. However, my budget is small (I've been stealing stuff out of my stash to do projects and haven't been replacing them) and I can't really afford an expensive yarn. I would try to go through a yarn manufacturer or knitting magazine, but the problem wth that is that they could reject it, leaving me with nothing. So, if I just make it myself, I probably have a better chance of getting it completed. So, are there any bulky weight yarns out there that aren't terribly expensive that wouldn't break my piggy bank but would let me purchase enough yarn to do said jacket/coat? I don't know how many responses I'll get on this, but I'll take what I can get. Any suggestions?