I wasn't referring to breaking the law of conservation of energy, but rather to the efficiency of the reaction. We would pay for more electricity to get a stable fusion reaction, more than we would get from years of harvesting energy from a single fusion generator. Plus the most readily available fuel, we think, is H-3 from the lunar regolith. Not something just lying around, then.
Where are you getting this information from? The most recent actual test is from JET, and it achieved 70% effeciency of the confinement energy, ~5% of total energy for a test run of about 20-60s, and this was in 1997. The currently being built ITER is expected to produce 10 times as much energy as is put into it, and once these reactors get going they would create the needed fuel source as part of the reaction chain.
H-3 as a radioactive isotope with a half-life of 12.32 years is not something that is mined or really found in nature as it decays very quickly. It is something that is produced, either from Lithium or from H-2, which is common enough in water for use. The needed fuel for a sustained nuclear fusion industry is just water, and there is plenty of water to last a very long time as the reactions only need a small amount. ITER expects a yield of 500 MW sustained for over 1,000 seconds with 0.5 grams of fuel, hardly making a dent in hydrogen reserves.