Welcome to the forum! $600 for a shooter Luger is a pretty good price. If they are not all matching parts/components, as Orv has indicated, they have no real collectible value. These Mauser Luger years byf41 and byf42 were high production years (well over 100,000 produced each year) so they are very common as military Lugers go. So then, the most important consideration is the mechanical condition of each Luger. First of all, you want the one with the best barrel bore meaning strong lands and grooves with no barrel pitting, frosting or corrosion. Or at least the one with the LEAST barrel bore damage. Second, (at the minimum) make sure you can rack or manipulate the toggle (cock it) and that the trigger goes click when you pull it and the safety lever works. If they were all matching specimens with very high remaining blue coverage and no external or internal corrosion or pitting you could well be looking at $1,200 to around $1,800 depending on the source, ie collector or dealer. Welcome aboard!