Is this for your personal residence? If yes, consider upping your badassity instead of immediately rushing for HVAC.
Because, if people are living there now, and you are considering living there, suggest you talk to them about how it's worked for them. You might be surprised, older house were designed with better air flow.
Full disclosure: We live without A/C in Central Texas, so I am thinking "Iowa would be a piece of cake compared to us". Price tag for full HVAC would be about 30k for us. Not worth it when we are healthier without it.