If you have to ask, you can't afford it???
I tell 'em that I charge X for a service call, and that will tell them what is wrong in most cases, then it'll be parts and the labor to install 'em to complete the repair.
If we need details, then it is service call covers the trip charge and 1/2 labor to diagnose. A trickier problem may include extra labor to get to the diagnosis, and the parts cost includes shipping and taxes. Labor is 1/2 hour minimum and billed to the nearest 15 minutes.
I also try to get an idea of the problem so that I can encourage them to do the repair. But I never tell them the problem. Its more like "No heat? Well, there are a few things that might cause that. Most are pretty inexpensive and straight forward to fix. It is definitely worth looking into.
If they want more details, I say "well, it depends upon the model. I can't really say for sure until I can [look, listen, check, test, try, run, diagnose, tickle, etc.] your specific appliance. Oh, the parts. Yeah, those vary. Can be as low as A or as high as M, sometimes, I've seem 'em as high as Z, but that is rare. Most times, a generic repair runs between this and that. But we really can't tell until I look at your machine."
I am always looking to improve my spiel. Hope others contribute some ideas here.