I've been wearing bifocal sunglasses / safety glasses for over 10 years, we used to have a COG member that had a site called sunglasses guy, but I can't find him, I bought 4 sets of those wraparound style units, that came with clear and dark bifocal lenses and 3 other shades, including amber night lenses, for about $20 delivered... well, they cost more now, as the demand seems higher...
quick google gave me these tho,
http://sunglassrage.com/bifocal-sunglasses/?gclid=CISJwN_qhcQCFQuBaQodK6gAHwstill, you can get what ya need..
personally I think paying $100 for a pair of glasses that don't come from an eye doctor is ridiculous... it's all in the name they carry, and if you drop them, or sit on them, you're out $100.... silly.
The best reading glasses I have cost $19, and I have progressive "Lacoste" framed main working glasses I paid $400 for from my eyedoctor, that really don't compare to the el-cheepo's... go figger'
just to note, I originally went in search of these when I was on the way home from a ride, and had to read maps on my tank bag map holder, so I was wearing mini reading glasses down low on my nose inside my helmet... well, after an hour in bright sun, scanning the map, and looking over the tops while riding, I realized the reading glasses were focusing the sun glare off the plastic on the map cover directly to my retina's... and the resulting sunburn and UV welding burn was obvious....
ouch...
no more of that nonsense, and unfortunately my progressive reading glasses (no mag on top, some mag in middle for computer screen distance, and lateral scanning, and high mag on bottom) simply recreate the intense retinal burn...
takes a few miles to get used to the bifocal sunglasses, but when you get them right, and simple scan down with the eyes to see the gps, it works really well.. oh, and refrain from the polarized ones... most modern helmet shields are polarized, and my helmet has a flip down internal tinted "aviator style" insert, which doubles the polarized effect... they don't mix with polarized glasses at all...
ymmv