The purse and bag themselves cost 0 $ to start.
That's wrong. By extracting them you lose the money you would've made from selling them directly.
The cost-efficiency needs to be determined by some changing factors:
The maximum amount of runts you can assign to any project
The amount of times you can repeat a certain project
Another project you can compare it to (considering you've the tech and infrastructure to do it)
We...
The maximum amount of runts doesn't matter because you calculate profitability per runt-hour.
The amount of times you can repeat a certain project can be separated into two categories: infinite and finite. Finite projects often have higher profitability and switching your runts around to accomodate that is strongly recommended, especially in the beginning of the game.
Comparing it to other projects is important for ranking them, not for figuring out the cost-efficiency.
And while my sheet is a tad outdated, the profitability of those projects is higher than that of any repeatable one, so you should always go for them. Treasure chest extraction is the single most profitable thing, Money Purse places 16th and Bag of Cash still comes in at 60th. Essence production is generally very profitable, as are some other animal extractions, disassembling plasma and nuclear lasers, and assembling most of the ship weapons.
Honorable mention also goes to extracting integrated devices, which places surprisingly high for its position in the tech tree and the times you can run it.
