I recently bought a house that turned out to have asbestos, some of it in the sheets covering a workshop that I knew about in advance, some of it in boarding under two windows that I didn't. It turned out not to be too expensive to have local professionals deal with it. If there are a lot of houses in your area with asbestos, there will also be specialist firms able to deal with asbestos. They should have no problem giving you a general estimate, or even coming out to inspect a house you are thinking of buying and giving you an estimate of the cost of dealing with it.
The advice I was given was: if it's in situe and covered over and you are not interfering with it, it can safely be left. If it's not covered over, it can safely be covered over and left. Otherwise, have it removed. The problems come when interfering with it: drilling holes, exposed dust, crumbling edges, and so on. I could have had the boarding in my house covered over, but it wasn't expensive to remove and as I'm renting it out and so had less control over it's future condition, I had it taken out.
I was also told that it is possible to remove asbestos oneself: damp it down to minimise dust, wear a good facemask, double wrap it and dispose of it to a proper waste disposal centre that accepts asbestos. I didn't do this because I could afford the reasonable cost of professionals and didn't think the risk was worth it to me.
The roofer told me that no roofer ever has had asbestosis: he thought that the combination of being outside in the open air and being above the asbestos rather than below it and having the dust coming down made the difference, but that is of course only anecdotal.