1 old 12V 500mA+ router PSU
1 white (4000-5000K) LED strip arranged in a square with an X in the middle
Thin wood and glue, create a flat 18x18x7 cm wooden box where the LEDs will go, wire everything, make a hole for hanging
Cover with an A4 sheet (for the diffuse effect) and then card stock or another A4 sheet on top if the light is too dim, at least 3cm between both
(optional) paint the wood so it looks better
Total: less than $200 for sure and like 5 minutes if you're fast enough to put everything together. It sure needs more details but that should be the basics, there's also a way to connect your "boxes" together, I'm thinking of something simple as two sets of male and female connector per side, the box with the PSU acts as master and the rest are daisy chained as slaves but it might need a bigger power supply, 2 or 3A depending on the LEDs and amount of boxes.
same working principle
anything is possible given enough time and not enough money