My local industrial surplus place has an old forced convection lab oven (for $35) that goes up to 280C/536F. The interior volume is 13.5"w x 11.5"d x 11"h. As a hobbyist, this strikes me as a good size for tempering tools (including hammers) and small to medium-size knives.

The temperature range seems a bit low for all the tempering I might want to attempt, but might this be a worthwhile addition to the shop? Or should I just stick with my five buck toaster over?

For $35 bucks, I'd go for it. Probably more accurate and consistent than a toaster oven.

I would get it. Most of our tempering is done between 350 & 400F. Can't beat the price either.