This is a pretty straightforward question:
How does $1,000 per microgram equate to $350 billion per pound, as stated in this column about the most expensive thing in the world? Since 1 kilogram equals approximately 2.2 pounds and the rest of the conversions are within the metric system, I fail to see how the 35 enters the picture.
1 pound = 453 592 370 micrograms
$43000000000 per pound, actually.
Maybe Cecil was using a troy pound, which is (approximately) 373,241,722 micrograms.
If you really want to know how much californium-252 costs, you can order some. “Quanity discounts may be available.” 
Since the sale of Californium-252 in question was quite a long time ago, I thought I should check the Internet for better prices. As I suspected, you can buy Californium cheaper than $1,000 per microgram, if anybody has any to sell.
On a site where most of the posts are in Russian I found a reference to a 1998 sale of Californium-252 for $56.00 per microgram.
Here is the paragraph:
The isotope Cf-249 results from the beta decay of Bk-249 while the heavier isotopes are produced by intense neutron irradiation of this product. Logically one would expect that Cf-252 would be more expensive then than Cf-249. However, in Sept. 1998 the ORNL Isotopes Division charged $180.25 per microgram of californium-249, and $56.00 per microgram of californium-252, indicating that factors other than ease of prodcution were setting the price. If Cf-251 could be manufactured in quantity for the 1998 sale price of Cf-252, then a critical mass would cost $11 billion.
As you may guess from this excerpt, most of this thread seems to be about building light atomic bombs using Californium-252. I won’t bore you with the details. It does not seem to be worth while building an $11 billion Californium-252 bomb when plutonium is so cheap and readily available. Relatively speaking. 
As an afterthought, I checked eBay for Californium-252. No hits.
I mean, really. I AM disappointed. Maybe if I tried one of the foreign eBays, I’d have better luck.