I once used 5 litres of He3 in an experiment I was doing...
5 litres at Standard Temperature and Pressure cost ~$2,000 back in 1998- this price may have been artificially low. He3 comes from the decay of Tritium (Used in some nuclear weapons)... The price of He3 then, in a free market, would reflect the amount of tritium available. I was told that the price of He3 was set artificially low... (This may or may not be true). So it is NOT a cheap substance... that 5 litres had to last me ~2 years....