To me, the number of days doesn't really matter as much as the number of kilometres.
If your tires/chain and oil are good before the trip, and your trip is less than 6,000 kms, you don't need to immediately factor bike expenses other than gas.
Still, even if you don't change tires on your trip, you are still wearing them and will pay for them eventually.
I figure my bike costs me 15$ cdn per 100km (gas, loan, insurance and maintanance), so a 6000km trip (for example) is costing 900$ just in bike expenses, whether you pay as you go (gas), monthly (insurance), or once in a while (tires or maintenance).
I ride an average of 750 km per day, so every 750 kms, I require 3 meals and a place to sleep. One of those meals is usually at a restaurant and I camp whenever I can, but use a motel when I need to wash, watch tv, or get there after dark (especially if it rains). All in all, it averages to about 50$ per day per person (every 750 km). For my hypothetical 6,000km trip, that would be another 400$ per person.
So a 6,000km trip is costing me 1,300$. to this, I need to add a fun budget for attractions I wish to see, an emergency repair fund if something breaks down, budget for extra nights in places I want to spend more time at, and I haven't had a single beer yet. If you're riding around the entire country, your distance covered is likely to be about three times that, so figure about 4,000$ (sans fun-budget).
I don't think Randy's out to lunch (or the Hilton) with his 5,000$. A lot of us just suck at guesstimating cost.
Oh, if you don't already have camping gear for your motorcycle, you can easily add another 1,000$ to the bill.
You can't use Zellers sleaping bags, they don't pack small enough, nor do their tents, and you can forget about carrying a campstove that doesn't fit in your coffee cup. Titanium cookware anyone?