Hic liber duobus sestertiis constat.

Here hic means this and is being used as a demonstrative adjective modifying liber. It must agree with liber in gender, number, and case, so the form is hic because liber is masculine singular nominative.

So:

• hic = masculine
• haec = feminine
• hoc = neuter

It is also worth noting that hic can sometimes mean here as an adverb, but that is not what it is doing in this sentence.

Liber is the subject of the sentence, so it appears in the nominative. The sentence is about the book and tells you what it does: it costs a certain amount.

So the basic structure is:

• hic liber = the subject, this book
• constat = the verb, costs
• duobus sestertiis = the price

Constat is the third-person singular present active indicative of constare.

That means it translates as it costs, because the subject is singular: this book.

Formally:

• consto = I cost / I stand together / I am established
• constas = you cost
• constat = he, she, it costs

In this sentence, constare is being used in the special sense to cost.

The phrase duobus sestertiis tells you that a price is being given. When constare is used with an expression of price, it means to cost.

In other contexts, constare can have other meanings, such as to stand firm, to be established, or to consist of. But with a money amount like this, the meaning cost is the natural one.

Because Latin uses the ablative of price with a definite amount. The sentence is giving an exact price, two sesterces, so the amount appears in the ablative, not the nominative.

That is why both words change form:

• duo becomes duobus
• sestertii becomes sestertiis

So duobus sestertiis means for two sesterces or more naturally at the price of two sesterces.

The forms duobus and sestertiis could look like dative plural or ablative plural, depending on context. In this sentence, they are ablative plural because the construction is one of price.

So the form is ambiguous by itself, but the syntax makes the function clear: constare + ablative of definite price.

Because duobus modifies sestertiis, and adjectives and numbers in Latin usually agree with the nouns they describe in case, number, and gender.

Here:

• sestertiis is ablative plural
• so duobus must also be ablative plural

This is the same basic agreement pattern you see elsewhere in Latin, such as hic liber.

A sestertius was a Roman coin. In this sentence, sestertiis is the ablative plural, meaning by two sesterces or more naturally for two sesterces.

You do not need to know its exact modern value to understand the grammar. The important point here is that it is a unit of money, which is why it appears in a price expression.

Yes. Latin word order is much more flexible than English word order. You could rearrange the sentence and still keep the same basic meaning, because the case endings show how the words function.

However, Hic liber duobus sestertiis constat is a perfectly natural order:

• hic liber keeps the noun phrase together
• duobus sestertiis gives the price
• constat finishes the statement

Latin often places the verb near the end, though it does not have to.

Here it is the noun meaning book. Latin also has an adjective liber meaning free, but context shows which one is meant.

In this sentence, hic liber clearly means this book, and the rest of the sentence talks about its price. So the noun meaning is the only one that makes sense here.