like the other bros said; scared then don't chiong.
but if you do want to, take note that STDs are not always transmitted. Look up the transmission rates if you're curious. If I'm not wrong, HIV has the lowest while herpes is the most contagious.
Barrier protection helps enormously, but they might break or you might get a virus that does not require genital-genital transmission (e.g. herpes).
My advice? jerk off before/while you look at the adverts. After you're done, you'll feel less like spending money.