If you Gents want me to produce a study, then sorry, there are none that I'm aware of. If you'll accept anecdotal evidence, then just do a simple search on the subject and you'll see cases of failure, and just as importantly, you'll see instances of wide temp flux with the cheap on/off thermostats.
If you have no worries trusting your collection to a $30 thermostat, then I also have no worries trusting your collection to a $30 thermostat. For my collection, I want better quality and function than what $30 gives me. That doesn't mean you're doing wrong, but, the OP did ask for opinions.
This statement seems a little incongruent with the picture you've painted about inexpensive on/off thermostats being all that is required for a rack system...
Wouldn't this course of action eventually render the initial $30 spent as useless? Wouldn't it also further delay the OP from purchasing an upgraded thermostat?