I am building some glass shelves across a window with is about 40+ inches wide for my plants. This is what i had in mind

I am thinking i'll need 1/4 inch thick tempered glass to hold the pots across that length -- is that enough?
Can you recommend a place where i could have a couple of these shelves made for cheap? I'm looking at something that's about 43" x 8" that's sanded down at the edges to remove sharp ends, nothing fancy. One place I priced in Dulles was quoting $50+ per shelf!
Any advice would be appreciated.
Thanks,
shireen