I did this same rough math a little while ago and came to the same conclusion… glad someone did the work in spelling it out – LED’s are neato, but way too expensive…
Shop lighting upgrade: T5 vs T8 fluorescent vs LED
I am in the process of upgrading the lighting in my shop. It currently has a number of 4-lamp and 2-lamp T12 4-foot fluorescent fixtures. The best solution is to replace the ballast in each of these fixtures with high-efficiency electronic ballast ($15), and replace the lamps with T8 high-CRI bulbs. This will save energy, and greatly improve the quality of the light. LEDs and T5 fluorescent are MUCH more expensive to install, and their energy savings are not nearly enough to justify the cost. Remember that running a T8 with an electronic ballast will provide more light than it’s nominal rating, which is for magnetic ballasts. T5 are always rated for electronic ballasts, so it is not a fair comparison.
For new fixtures in my shop, the cheapest/best solution is to buy $10 "shop lights" and replace the ballast. The total fixture cost is $25, and efficiency is 96 lumens/watt for a total output of almost 6000 lumens. It can’t be beat! Commercially-available T8 fixtures with electronic ballasts are more expensive, and the quality of the ballast is suspect.