All three have "PDF" search equivalents (e.g., "Menschen A1 Kursbuch PDF digital"), and they are often cheaper than Netzwerk.
If you cannot buy both, buy the Kursbuch (digital) and look for the Arbeitsbuch answer key PDF online (often legally free from teacher forums) to check your written work. kursbuch netzwerk a1 pdf
If you are looking for supplementary materials or digital versions of the textbook rather than a research paper: Digital Textbook & Manuals All three have "PDF" search equivalents (e