Current thoughts:

Note: The Orcish Ziggurat tooltip says “Gold, Mana, and Knowledge” but actually gives happiness, not knowledge.

Consuming the builder to create a gold mine feels good - more balanced and interesting to me than the alternative, since it makes increasing gold income something that a City must do. However I don’t like that gold is unique in this respect; it’s slightly counter-intuitive that this one resource should be a special case.
After some reflection, I think basic structures that produce Gold, Mana, and Knowledge - i.e. the three resources that accumulate to your empire and not just the city itself - should all consume the builder and take 1 turn. So builders can spend time to improve a city, but it takes a city’s time to improve the empire.

Current Price: 5g per 10 production, 2 Turns.
Recommended Price: 7g per 10 production, 2 Turns.
Farms are super useful even from the very beginning of the game - mainly just due to the low price. Recommend to boost cost from 5g per 10 pop to 7g per 10, just so it's not quite such a no-brainer in the opening turns to build this over anything else.

Current Price: 25g x production, 1 Turn, consumes builder
Recommended Price: 20g x production, 1 Turn, consumes builder
Instead of thinking "when will I break even" I prefer to think in terms of “time to double your money”. Priced at 25g per gold produced + the builder means it takes close to 40 turns to double your money invested even with the best morale...this seems high, compared to the time it (generally) takes a new city grow and pay back double the gold invested in its settler and buildings. Of course that depends on tons of other factors that can boost the growth or income of new cities, as well as the territory involved. But that’s the choice a person who wants more gold has to make: builder or settler. And right now settler is winning by just a little too much IMO. Recommend price to be reduced just slightly to 20g per gold produced.

Current Price: Confusing! Seem like they all cost a total of 250 resources regardless of yield?
Recommended Price: (5g+12m) x production, 1 Turn, consumes builder
Considering that mana income is far easier to get from buildings and far less valuable to stockpile than gold, this should be less expensive and paid mostly in mana. Mainly, needs a consistent cost/yield like other resources.

Current Price: 20g x production, 3 Turns.
Recommended Price: (7g+10m) x production, 1 Turn, consumes builder
Recommend to balance this closer to the costs of knowledge generating buildings (including consuming the settler), and include mana as a big part of the cost.

Current Price: 30g x production, 3 Turns.
Recommended Price: 12g x production, 3 Turns
Production is cool…but your ability to actually use it is severely limited by (1) the fact that you can only make 1 thing per turn no matter how much you have and (2) the fact that you usually run out of gold and end up making merchandise from time to time anyway. And to go from producing “big” ~250 hammer items in 2 turns, like most metropolises naturally do, to making them in 1 turn takes a TON of production…I tried building one or two extra quarries at my capital and regretted it - made no difference at all to most build times. Given that, 30g per production is just way, way too much. The least efficient production building, Master’s Guild, adds production at ~17g each and also gives multiple other benefits including unlocking the Grand Palace. Recommend price to be 12g per production.

Current Price: 350g + 10g per 10 happiness, 3 turns
Recommended Price: 50g + 15g per 10 happiness, 3 turns
I don’t think the value of being able to buy units from an inn is anywhere near 350g. The units themselves are over-priced and usually worse than what you can produce or summon. The happiness itself, on the other hand, is quite valuable. Even if you have max happiness already, it can give you leeway to rush production more often.

Haven’t had a chance to try them all…mostly these prices seem pretty good/fair though.