Coursera features a monthly cost, meaning that it can cost more than edX! Typically, most edX courses are free, and you will only need to pay a small fee for the certificate or any exams you need to sit. The one-off payment can work out as cheaper for some users and means there is no monthly rolling cost that you need to worry about.
However, some courses on edX will need to be paid for and can work out more costly than Coursera; it all depends on the courses you want to undertake! The courses on Coursera tend to be accredited more often than those on edX, meaning for some people, the cost is worth it.
To work out which one is best for you, consider the pricing of both and look at the courses you are interested in. it might work out as cheaper to pay the monthly costs or the one-off payment depending on your budget.