Unless you play with map contacts on, then there is no easy and reliable way for determing range (unless you have sonar or radar).
So basically the answer is to use the stadimeter and practice getting good results
but actually, it's very worth learning to get a hang of AOB by eye. Many here consider it to be an arcane art that is near impossible. I disagree, however, and I have come to expect my visual AOBs to be accurate to 5 degrees.
there is a thread here giving a walk-through the various AOB positions, and you can use the AOB to improve the reliablity of stadimeter/range estimates for purposes of getting speed
http://www.subsim.com/radioroom/showthread.php?t=134200
and once you can do it a plot can be made which looks like this