Check the prices on high quality sunglasses - $139 is pretty cheap.
The last time I was in Maui I bought 3 pairs (my 3rd, 4th and 5th) of Maui Jim's at a great price of $175. They're
$162 for used on eBay right now. (
other Maui Jim prices)
Any of the good brands (Oakley, Maui Jim, Ray-Ban, etc) are in the $150-$250 range. Go for the "designer" stuff (Gucci, Bvlgari, Ralph Lauren, ...) and it's easy to double that price.
You can save money buying from one of the rotating sunglass displays at Walmart, but wouldn't you rather be sure that your sunglasses block all the harmful UV rays, and eliminate glare (Maui Jim uses 9-layer polarizing filters, bi-gradient reflective coatings, and anti-reflective coatings).
If you spend a bit more to buy an Apple, why not investigate quality items for your other purchases?