The "uranium reserves" figure is not like "oil reserves", because it grows exponentially with the price you are willing to pay, (oil tends to grow too but the growth figure is very quicly reaches the natural limits).

From Wikipedia:

The ultimate supply of uranium is very large. It is estimated that for a ten times increase in price, the supply of uranium that can be economically mined is increased 300 times. See World Uranium Resources.[9]

http://en.wikipedia.org/wiki/Uranium

To say that "we have several decades of uranium left" is like saying "we have only 100 days of food left in the world" (which can make you want to shoot yourself if you don't give it a second thought).

We are nowhere near to reaching the geological limits because what is being included in the official reserves now is just the tip of the tip of the iceberg. This link for example gives more than 100 years of U under 130$:

http://www.inb.gov.br/english/reservasMundiais.asp

But this is again relative, because should U go to 100$ and above (from the current ~ $35), the breeders reactors will become competitive, meaning that you have to multiply these figures by a factor of 100. In addition many new discoveries will be found all around the world if we simply start looking for them. Even now enormous amounts of nuclear fuel are simply stored away as waste, because the processed nuclear fuel contains plutonium and unburnt uranium that can be used. But the prices are so low that it is not worthed the investment and overcoming the NIMBYSsm.

Regarding economics - even at $130, the price of fuel will be below 30% of the production costs, assuming (wrongfully of course) that the sales prices in 100 years will remain at current levels.