I don't have many answers for you, but can add a few things. Costs are going to vary depending on what part of the country you were in. I was paying $2.50 a blade when I lived in Ohio and then moved to NY and it was $5 seven years ago. With that $2.50 I also had free name etching, and not some free hand engraver, it looked like I had taken my blades to Things Remembered and had it all done. I did LOVE that, especially working in a multiple grooming salon.
There are a lot of sharpeners out there, but NOT a lot of really good ones from my experience. It really seems to take a special knack. I don't understand all the ins and outs, but I have tried SO many sharperners over the 15 years I've been grooming and have only found 2 fabulous ones (have never tried the ones on this board though). Here we have one sharpener that charges $15 per shear, then another that charges $7. I also believe you need to sharpen a convex blade differently than a beveled edge. Some shears have a corrugated edge and it ticked me off to pieces when I had a sharpener corrugate all my shears! I think if you can find hands on training it could be wonderful. If you have the knack, and do a fabulous job, well, you'll be in high demand. A great sharpener is worth their weight in gold. I wouldn't want to just have a video or manual to read to do this though.
I know the one sharpener I use charges more for beautician shears because they require a different kind of edge according to him. He charges $20 a shear for them. So if you can learn to sharpen both grooming shears/blades and barbers shears/blades you will expland your target customer base.
I actually prefer to have my stuff sharpened on site while I wait. i don't mind paying more for it either. I tend to wait too long before I call the sharpener and want them back ASAP, so having him come right to the shop was always great. Now being mobile, I find out when he's going to be at the shop I used to work at and wait there or send them with my employee when she goes to dog shows as she has found a GREAT sharpener. My equipment has never been sharpened so well. Takes a lot to make me go "WOW" when I put on a freshly sharpened blade, because I expect them to work. This mans work WOWS me!
What a caterpillar considers the end of his world, we call a butterfly.