"How much is this?"
I think you're right that in typical situations you would be fine to omit the これは as the context would probably be understood, however since we're translating a single sentence without context here we need to take some extra care.
For this example, the sentence "How much is this?" tells the reader that the speaker is probably holding or pointing to an object that is close to them.
The sentence「これはいくらですか。」tells us this same information with the use of これ.
If you only write 「いくらですか」 then we lose that information. It might not seem like a big deal right now but trying to be as accurate as possible with translations early on will probably help a lot later on in your studies. Let's all keep doing our best!