This is an easy one... I bought the Dremel chainsaw sharpening accessory tool a few years ago and can resharpen a chainsaw blade in about 4-6 minutes. It may not be pure professional quality, but it sure makes a big difference and it is good enough for me.
Note - because I was frequently hitting the dirt with my blade(s) since I was flush cutting hundreds of trees in my CRP acres I would have went broke getting them sharpened for a fee. I now maintain 2 "beater" blades that I have sharpened many times, one of which is nearing the end I think. I also have one "good" blade that I never let hit the dirt, yet, and I resharpen that one too, I just take a little more time to do so.