"I understand that it's, you know, for national security but, you know, it's... they're kind of pricey. Just a little bit, but I guess it's worth it," said Flores, of west El Paso.

Getting a passport doesn't come cheap. It costs nearly $100 for an adult. Starting Thursday, either a passport or a birth certificate, a much cheaper option at $23 a copy, will be required to cross back into the U.S.

"All of last week and this week we've seen lines out the door. So, and they're asking for birth certificates," said Elizabeth Frescas with the El Paso County Clerk's Office.

Many have heard the news and already have their paperwork in order.

"They've been telling me for a while. So, you know, I'm ready for it. I have my birth certificate, I have my ID, I have everything ready," said Alfred Vasquez, of downtown El Paso.

While many are familiar with the new rules at the border, it does come with a price. It's giving some second thoughts about crossing over in the future.

"If you tell them you need a passport and they don't have it, they ain't going to go visit. They ain't going to stop here in El Paso to leave a little bit of money, you know, it's going to affect the economy all over," said Vasquez.

Starting in February, U.S. citizens will also be able to apply for new passport cards. They'll be about half as much as regular passports, wallet-size, and fulfill the same citizen ID requirements at the border.