At some point I needed to read a computer monitor and small-font PDA at the same time, so I made a pair of bifocals for $4
This is almost trivial:
1. Buy 2 pairs of identical frameless glasses in 2 different strengths
2. Cut both pairs across horizontally with a hacksaw
3. Sand the cut edges of the lenses so that they are flat and match up (they won't match exactly because the stronger lens is
4. Glue the bottom half lenses from one pair to the other pair using epoxy resin.