Well, first of all, the plan I assume you’re referring to is going to cost about $674B:
http://www.foxnews.com/story/0,2933,74807,00.html
Secondly, the way they figure out the costs on something like this isn’t quite the same as, say, the way you figure out how much you’re paying for your car, by counting X payments of Y dollars each and coming out with a total. This plan isn’t going to “cost” $674B in the sense that the government is going to be writing $67.4B checks every year for the next decade. That figure represents how much less the government will be receiving in tax revenue over the course of the next decade. And even then, the way they calculate numbers is pretty basic - they simply say, “Well, right now X number of people are paying Y1 in taxes, and if lower taxes, X number of people will be paying Y2, so we’ll onyl make Z.” In reality, lowering taxes generally increases the overall taxable income in this country, such that the real “cost” of the tax cuts is going to be substantially less than $674B. In fact, it’s possible to cut taxes and have tax revenue increase, depending on circumstances. That may or may not happen here, but regardless, the tax cut portion of that $674B is going to cost less.
So, getting back to your question, if you keep in mind that the cost of this package is mostly just a loss of tax revenue, should it take 10 years? Well, it kinda has to, by definition. Calculating the cost that way, the revenue loss can be seen to be arbitrarily large, depending on how far ahead you look. It’s $674B over 10 years, maybe something like $1.5T over 20 years, and infinite over an infinite number of years.
Now, there are elements of this stimulus package that don’t involve tax cuts, but the only one I can think of offhand is the unemployment benefits scheme (which is pretty clever, IMO). And that’s only a few billion, and will be payed for over two years, so it’s pretty trivial from the POV of the OP.
Anyway, I hope that answers your question at least a little.
Jeff