Amazon has a 'budget-friendly' Prime option for low-income customers — but it's actually a trap (AMZN)

Amazon Prime just got more expensive for some of its members.

Today, the online store announced it would be increasing monthly Prime membership rates from $10.99 to $12.99, which comes to around $156 a year.

These changes are likely to impact its lower-income shoppers who can't afford to pay the one-off price of $99 for a year-long membership.

Moody’s Lead Retail Analyst Charlie O’Shea said in a statement that Amazon's monthly deal "still affords members a more budget-friendly option, with the ability to ‘flex’ the membership as they see fit.”

But he also noted that the new increase means that monthly subscription members will be paying a 57% premium over yearly members – at nearly $60 extra a year.

Low-income shoppers are often stung with higher prices by not paying one-off fees. The same is true in discount stores, where those that can afford to buy in bulk are offered bigger discounts. A research paper done by two Michigan University professors in 2016 showed that low-income shoppers can end up paying about 6% more per sheet of toilet paper if they don't buy in bulk, The Atlantic reported.

Amazon does not disclose how many of its members pay on a monthly basis versus yearly, but this price increase could encourage customers to switch and pay the one-off annual fee. However, this isn't an option if you don't have the disposable income to cover it.

A survey of 7,000 people across America done by