Originally Posted by Luke
The stock springs will work. Most people never touch them. A stiffer front end will help most on downhills and in deep sand. A stiffer back end will help with a heavy load. It's also important to keep the springs balanced- being soft on one end and stiff on the other is probably worse than being soft on both ends.
Since you're on a budget, I'd say start with the stock springs, load up the bike and try to ride it in as many different conditions as you can. If you don't like how it handles in a given situation, fix it. Get all the free adjustments (preload and damping adjusters) dialed in, then if that isn't good enough start changing parts.
I totally disagree the stock springs need to be replaced in this application. It makes the bike a lot safer to ride and more comfortable. It is the most basic suspension adjustment. You can click your clickers all day long and it still will not be close to right. A big guy + a heavy load will not work with the stock setup. Winding down the preload only gets you so far. It does not alter the final rate of the spring. Springs are not super expensive. I would choose that over any other farkel you could imagine.