Ok, so that's where the problem lies.

Today there aren't very many bitcoins offered at $5 or less.  The Mt. Gox Live chart shows only about 25,000 bitcoins offered for $5 or less on that one exchange.  Sure there are other exchanges, but the vast majority of bitcoins offered for sale are still listed on Mt. Gox.  And there isn't much interest from people willing to sell their bitcoins for $5 or less.
 - http://www.mtgoxlive.com

If you wanted to buy in one fell swoop every bitcoin offered for sale on Mt. Gox no matter what the price is, that would only find 270,000 BTC offered (though over time additional offers to sell at the higher prices would certainly begin to appear).

 - http://bitcoin.clarkmoody.com
 (click on Show Calculators and then enter a few million dollars in the Buy Bitcoin field.)

Here's the entry in the FAQ that answers your question:
 - http://en.bitcoin.it/wiki/FAQ#What_if_someone_bought_up_all_the_existing_Bitcoins.3F

So, if you were intent on spending every last bit of the lotto jackpot money on bitcoins, that would be possible as new sellers would emerge when the values got higher but you'll run out of your lottery money long before all the sellers run out of all their remaining bitcoins.