The energy cost of obtaining Deuterium and Lithium is minimal compared to the energy released by the fusion process. There are many references that provide relevant information but a sensible one to refer to is the official ITER site "Fusion for energy". Fusion for Energy (F4E) is the European Union’s Joint Undertaking for ITER and the Development of Fusion Energy.
On their understanding fusion page they say:
A 1,000-megawatt electric fusion power plant would consume around 100 kg of deuterium and three tonnes of natural lithium in a year whilst generating 7 billion kilowatt-hour. To generate the same amount of electricity, a coal-fired power plant would need around 1.5 million tonnes of coal.
and
If used to fuel a fusion power station, the lithium in one laptop battery, complemented with half a bath of water, would produce the same amount of electricity as burning 40 tonnes of coal.
(eg ~= 8000 dollars at 5c/kWh wholesale or 40,000 dollars at NZ 25c/kWh retail).
However what is required is Tritium - Lithium is simply an easily obtained precursor. Obtaining Tritium from Lithium is the "hard part" and while it is proposed that this step be incorporated in the ITER system, and is liable to succeed if ITER succeeds, the process is at this stage "theoretical and experimental".
Tritium can be, and currently is, bred from Lithium using fast neutrons from existing reactors, the amount obtained in this manner is enough to initiate a national or international fusion energy system but nowhere near enough to sustain it. What is essential is the "breeding" of the essential Tritium from Lithium using a suitable source of fast neutrons from the ITER process itself
ITER's own site, in the section Tritium Breeding says
... While deuterium can be extracted from seawater in virtually boundless quantities, the supply of tritium is limited, estimated currently at twenty kilos. .... tritium can be produced within the tokamak when neutrons escaping the plasma interact with a specific element—lithium—contained in the blanket. This concept ... is an important one for the future needs of a large-scale fusion power plant.
ITER will procure the tritium "fuel" necessary for its expected 20-year lifetime from the global inventory. But for DEMO, the next step on the way to commercial fusion power, about 300g of tritium will be required per day to produce 800 MW of electrical power. No sufficient external source of tritium exists for fusion energy development beyond ITER, making the successful development of tritium breeding essential for the future of fusion energy.
ITER will provide a unique opportunity to test mockups of breeding blankets, called Test Blanket Modules (TBM), in a real fusion environment. Within these test blankets, viable techniques for ensuring tritium breeding self-sufficiency will be explored.
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How Tritium is obtained at present:
Construction & Operation of a Tritium Extraction Facility at the Savannah River Site
Final Environmental Impact Statement
DOE/EIS-0271 1999 - 140 page pdf
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With respect to generating hydrocarbons from "other sources of cheap energy"
Yes. The process could be totally "geologically stored hydrocarbon" free, which I think is the 'spirit' of what you are asking.
Once you achieve "energy too cheap to meter" [tm] (2nd time lucky perhaps) you can produce hydrocarbons from current biological waste - or from newly grown feedstock if you so desired. Various people have demonstrated 'just about anything organic' to petroleum products converters. Videos of some such are available on you-tube - caveat emptor as ever, and I knew a man in Louisiana who I have lost touch with who was doing just this several years ago, and having a lot of trouble interesting anyone in the process.
