The cost of an Amazon Prime membership could potentially rise next year and be a boon for the e-commerce giant's net sales, according to J.P.Morgan analyst Doug Anmuth.

Amazon is doubling down on Prime Day. The retail giant's marquee shopping event kicks off July 8 and will run for 96 hours, twice as long as last year's. The move has Bank of America making a bold sales call: Amazon could rake in more than $21 billion in gross merchandise volume (GMV).

Experts predict shoppers could see a $20 spike in Amazon Prime memberships. JP Morgan analyst Douglas Anmuth found that Amazon customers may need to pay $159 instead of the usual $139 annually for a Prime membership starting next year.