While looking for High Frontier 4 All resources, I found this neat mission planner by nornagon which allows you to pick a starting location and then see how many burns it takes to get to any destination: https://nornagon.github.io/hf-mission-planner/

Unfortunately, it appears that the map tool only optimizes for the least number of burns. This makes the tool less useful when you want to optimize for the least number of turns or hazards or some other balance of characteristics (see nornagon/hf-mission-planner#4). It also doesn’t appear to implement the Solar Oberth Flyby (see nornagon/hf-mission-planner#9).

However, it was still really useful to quickly see how many burns it actually takes to get somewhere and I was surprised to find that some sites in the Saturn and Jupiter heliocentric zones were much closer than I thought.