The first meaning for " cōnstāre" (cōnstō) is to stand together, you're right.
con (“together”) + stō (“stand”).
There are several meanings listed for this verb, for instance, to cost money, or to cost with a figurative meaning, like costing pains, etc...
Meanings that are listed (wiktionary):
to stand together (also the etymological meaning)
to stand still; to remain the same; stand firm
to agree, correspond, fit
to be certain, decided, agreed upon, consistent
to consist, to be composed of
I've found a part of the answer you asked, though a dictionary entry with dates.
Plautus and 2nd century BC.
to stand still, (to stand with?)
Cicero and 1rst century BC
to subsist (to maintain oneself, to be), to exist (to survive?)
CONSTAT (ALICUI, INTER OMNES) + infinitive proposition
1rst century BC (Cicero)
it is an established fact that, (for someone, for everyone)
CONSTO, AS, ARE, STITI, STATURUS, intr (+ ablative)
1rst century BC (Caesar)
cost v. intransitive: to cause penalties, sacrifices.
CONSTO, AS, ARE, STITI, STATURUS, intr + ablative 1rst century BC (Lucretius)
to be constituted by.
CONSTO, AS, ARE, STITI, STATURUS, intr + dative
1rst century BC (Cicero) to agree with
CONSTO, AS, ARE, STITI, STATURUS, intr + price in genitive
1 century BC (Cicero)
cost v. intransitive, to require a payment to be acquired: cost.
CONSTO, AS, ARE, STITI, STATURUS, intr EX + ablative
1rst century BC (Cicero)
to be composed of.
to consist of
CONSTO, AS, ARE, STITI, STATURUS, intr IN + ablative 1rst century BC (Caesar)
to depend on, (to rest on)
CONSTO, AS, ARE, STITI, STATURUS, INTR PARVO, PLURIS 1rst century BC (Seneca)
Your right. It's quite interesting. I may add to that , that we had a classical Latin and later on a modern one .The Latin of the decadence period is associated with the fall of The Roman Empire. Plauto's Latin is one of the classical ones, and so is Oratio's and many more. In the Italian schools, they teach the modern Latin.
Shouldn't "quanti" agree in case, number, and gender with "olivae?" If so "quanti" should be "quantae."
No, quanti is always used like this when it means a price. It's a genitive (singular, always), from Quantus. A fixed expression when it's used to ask a price.
You can think about it as "the amount's price", the price of the quantity, as quantus is "the (uncountable) quantity/how much".
In English Where/what/who are interrogative adverb, and also adjectives.
-Quanti is the genitive of value here, used to ask for a price. It's a fixed expression.
-Quantus is the interrogative adverb meaning you ask for "how much", an uncountable quantity. How much do you love me, etc...
-Quot is the interrogative adverb meaning you ask for "how many", a countable quantity, requiring a number. 20 men, 60 candies, etc...