Fleabay usually sells it for $17+ used for very limited qtys, and buy at your own risk.
Just wanted to upgrade an old Macbook pro 2012 (with 1 faulty ram slot despite the pressure fix.) at minimal cost.
So picked up a 4gb Transcend ddr3l 1600mhz stick from my local CEX. They had 10+ of the same model. Since its faster than stock memory and can run at lower voltage it has more chances of working in a Macbook Pro.
However, different stores will have different brands; YMMV. If 1600mhz is not your thing, 1866mhz goes for $1 more.
Shop in store, don't worry about shipping damage or lost packages. Keep your receipt for refunds if you encounter incompatibility.
There is a delivery charge of $3.00 per individual item valued up to $20.00. Any individual items purchased over the value of $20.00 will not incur a delivery fee