It's personal preference but things like arch support, heel cup, toe protection, midsole pedal platform, and of course sticky rubber make a dedicated flat shoe will worth the extra money. Prices are getting crazy though. I want the new 2fo which msrp at 160! When I started riding flats impacts sold for 90 bucks. Inflation does not account for the price increase, nor does materials used. In fact we get thinner sticky rubber soles these days that chunks out faster. More money, shorter life span, progress!
You can find a dedicated shoe that isn't popular greatly discounted. As long as it doesn't say 5.10 you've got a good chance of scoring a deal especially on a recently discontinued model. Even the crappiest sticky rubber flat shoe will grip better than a skate shoe. The market is flooded with flat shoes, many of which don't sell well. There are some great deals out there for someone that isn't stuck on brand or shoe model.