Industrial Enchantment

Industrial Enchantment first appeared in Classic: Technomancer and "were later made generic in GURPS Magic Items 3, which expanded them to fit into any setting at any tech level" and was updated in the Pyramid 3/66 article "Thoroughly Modern Magic".

Basics

The assembly line itself is a magic item "costing 10 times that to enchant whatever item it makes, multiplied by the square root of the number of mages who can work there." Classic: Magic Items 3 expanded the rules to all TLs and Thoroughly Modern Magic adjusted them for 4e. The time an item takes to make is (Normal energy cost/Number of mages/Efficiency)

A table with the components of Efficiency, Expenses Per Hex, Daily Wage, Daily Cost Per Hex, and Item Cost (Per Energy) is provided to reduce the number crunching. All that really is needed are the Efficiency and Item Cost (Per Energy). In a typical TL3 fantasy setting with plentiful wizardry and shops full of magic items the base commission is about $33 per energy point in addition to the cost of the materials to make the item being enchanted. The information on Paut elixir links this price to starting wealth. This shows that Industrial Enchantment (The green cells) is impractical in terms of cost below TL 2 though it does save time. The mark-up at TL 2 to equal commission Retail cost is slightly more than 25% which makes it a good baseline Retail Cost for TL3 and above.

TL	2	3	4	5	6	7	8	9	10	11	12
Starting Wealth	$750	$1k	$2k	$5k	$10k	$15k	$20k	$30k	$50k	$75k	$100k
Retail Cost (1/30)	$25	$33⅓	$66⅔	$166⅔	$333⅓	$500	$666⅔	$1k	$1⅔k	$2½k	$3⅓k
manufacture cost	$19.94	$23.41	$23.27	$23.96	$23.40	$25.47	$28.83	$35.23	$41.10	$57.95	$76.17
w/ 25% markup	$24.93	$29.27	$29.09	$29.95	$29.25	$31.84	$36.04	$44.04	$51.38	$72.44	$95.22
Efficiency	2	2	2	5	8	10	12	15	20	20	20

Assuming TL8 for the above 2,400 carpet, it would cost $69,192 to make and retail for $86,490 (assuming 25% markup) making it on par with higher end luxury cars.

Some key things to keep in mind

• The "assembly line" must have a mana adjusted Spell Power of 15 or higher to work.
• Must have at least one hex of floor space for every mage it is designed to accommodate. For the purposes of space calculation a hex is 93.5. For objects larger then a hex "multiply the total number of hexes in the line by 2 or by the square root of (the product’s volume in cubic feet divided by 93.5), which ever is greater".

• Assembly Line mage: average job but because of the requirements they earn the higher end of that category.
• Operational expense: 0.833% of the starting wealth x every hex of space in the line; fixed cost
• Success rate: 95.47% for a skill-15 line.
• Work month: 22 days (~5 day work week)
• Daily Cost Per Hex: Expenses Per Hex + Daily Wage
• Total manufacturing Cost: (Daily Cost/0.9547)/efficiency)*energy cost of the item.

GURPS Fantasy assembly line

Limited to making one kind of item this has a energy cost twice that of setting up a magical workspace to build a prototype item, or (number of prerequisite spells +1) * (800 energy points). "It turns out one copy of the prototype in (energy cost of enchantment/4) hours. Each mage working on the line can contribute 10 energy points per working day, reducing the cost of hiring mages." Using the four-man flying carpet (3 prerequisites) example above the item takes 600 hours (75 working days) to make (2400/4) but there are two conflicting results regarding the energy cost: 4,800 (2400 x 2) or 3,200 ((3+1) x 800)).