If I run several GPS tracking apps at the same time, like strava, ski tracks, my tracks, for example, does the battery drain much faster then using a single gps tracker? Basically what I'm asking, is how much of the gps battery usage is from the communication to the gps vs how much from the individual app usage.
The GPS itself probably won't use much more power – after all it doesn't matter if 1 or 100 apps ask for the location: it's obtained once and then handed to all. Actually there's even a "location cache": if you're now at e.g. Trafalgar Square in London, you're unlikely to be in Manhattan the next second (exaggerating a little) – so that's what subsequent requests within a short interval access. And that's also what's used when you e.g. enter a tunnel and temporarily have no location info.
A little more power of course will be required as the device is kept awake "more aggressively": one app probably would update the location once per second (or fewer times) – while multiple apps won't do that "unisono" (at the exact same time). But compared to the overall load while tracking (or navigating), that's most likely rather a little indeed.
Which reduces your question to: "Does using multiple apps use much more battery". The answer to that is "it depends". It certainly uses more – but how much depends on what those apps do, how well they are written, etc. Also think of ads they may draw, or data uploads they might perform.