Ganz gleich, ob die Maßanfertigung teuer ist, prüfen wir sie.

Ganz gleich, ob is a fixed expression meaning something like regardless of whether or it makes no difference whether.

So the structure is:

• Ganz gleich, ob ... , ...
• Regardless of whether ... , ...

It introduces a contrast that does not affect the result in the main clause.

A close everyday alternative is egal, ob.

Because ob introduces a subordinate clause. In German, the finite verb usually goes to the end of a subordinate clause.

So:

• die Maßanfertigung teuer ist
• subject: die Maßanfertigung
• predicate adjective: teuer
• finite verb: ist → placed at the end

This is normal after conjunctions like:

• ob
• weil
• dass
• wenn

Because the sentence begins with a subordinate clause:

• Ganz gleich, ob die Maßanfertigung teuer ist, ...

When a subordinate clause comes first, it takes the first position in the overall sentence. In the following main clause, German still keeps the verb in second position, so the verb comes immediately after the comma:

• ..., prüfen wir sie.

This is the same pattern as:

• Wenn es regnet, bleiben wir zu Hause.
• After the subordinate clause, the verb of the main clause comes first.

So prüfen is in the normal V2 position of the main clause.

Here ob means whether, not a normal conditional if.

So:

• ob die Maßanfertigung teuer ist = whether the custom-made item is expensive

English often uses if and whether in similar ways, but German usually distinguishes them more clearly:

• ob = whether
• wenn/falls = if in a conditional sense

In this sentence, the idea is not a condition like if it is expensive, then...
Instead, it means whether it is expensive or not, we check it.

Maßanfertigung is a feminine noun, so its article is die.

It means a custom-made item, made-to-measure product, or custom-made piece, depending on context.

It is built from:

• Maß = measure / measurements
• Anfertigung = production / making / fabrication

Together, it refers to something made according to exact measurements.

Because Maßanfertigung is a feminine noun, and the pronoun referring back to it is sie.

In the main clause:

• prüfen wir sie
• sie = the custom-made item

Here sie is in the accusative, because it is the direct object of prüfen.

For feminine singular nouns, the nominative and accusative pronoun are both sie:

• nominative: sie
• accusative: sie

So even though English would say it, German uses sie because the noun is grammatically feminine.

Because teuer is being used as a predicate adjective, not as an adjective directly before a noun.

Compare:

• die teure Maßanfertigung → adjective before a noun, so it gets an ending
• die Maßanfertigung ist teuer → predicate adjective after sein, so no ending

In your sentence, it is the second type:

• die Maßanfertigung teuer ist

So teuer stays in its basic form.

Because German normally separates a subordinate clause from the main clause with a comma.

Here:

• subordinate clause: Ganz gleich, ob die Maßanfertigung teuer ist
• main clause: prüfen wir sie

So the comma is required.

German comma use is often stricter than English in this kind of sentence.

Yes, that is possible, and it sounds more conversational.

Compare:

• Ganz gleich, ob ... → slightly more formal or polished
• Egal, ob ... → more everyday and informal

Both mean roughly the same thing here. The grammar stays the same:

• Egal, ob die Maßanfertigung teuer ist, prüfen wir sie.

It is in the nominative inside the subordinate clause, because it is the subject of ist.

In:

• ob die Maßanfertigung teuer ist

the structure is:

• die Maßanfertigung = subject
• ist = verb
• teuer = predicate adjective

Then in the main clause, the same thing is referred to again by sie, which is accusative because it is the object of prüfen.