OK, here's my report: the $12 1/4" glass works great.
No doubt all these other ideas are good, too, but this was the most convenient. Last night was the first time I've ever sharpened a tool, so the brand new $20 block plane from HD was the only thing to practice on. It did get very sharp, but I apparently need to (a) get the blade at a perfect right angle in order to get an even grind, and (b) pull out all of the staples that are still in the lumber.
Thank you everybody for your adivce.
Eric