If your shoes are strictly for commuting (meaning, you have another pair of shoes ready for you at your workplace), you can't really go wrong with a pair of short rainboots (Loeffler Randall makes some lovely versions). As long as you size up and wear them with socks, you shouldn't feel overheated.
However, if these are shoes that'll need to last you all day, you're also in luck. There are tons of jelly sandals and flats that range from cutesy to professional, and most ring in under $100. Find one with a thicker sole and a closed toe to minimize in-shoe slippage.
Melissa For J. Crew T-Strap Sandals, $70, available at J. Crew.