A lot. Had Zaphod deposited £0.01 in a bank on Ursa Minor Beta before visiting the Guide offices, and had he earned one ten-millionth percent interest annually over the five-hundred and seventy-six thousand million, three thousand five hundred and seventy-nine years that Marvin had waited for him, he would have had £1.42 x 10^248 with which to pay his dinner bill. It seems that "fabulous cost" does not quite do justice to the expense of eating at the Restaurant at the End of the Universe. In fact, were Zaphod to withdraw all his money in bills of denomination £10^219, he would be able to, in principle, lay his money from one end of the observable universe (at that time) to the other. Were Zaphod to attempt to withdraw his money in bills of denomination £10^191, the bank would be unable to comply with his request, as the observable universe at that time would not contain the mass required to supply him with so many bills.

From the alt.fan.douglas-adams FAQ.