A: Diaphragms are much cheaper, clocking in at around $75, to an IUD’s $1,300. But IUDs (Intrauterine Devices, in plain English) are far more effective at preventing pregnancies: how effective, you might be asking? 99% effective. But remember, the only thing that’s going to protect you from an STD is a condom. So be sure to use both barrier methods in combination with one another.