Roundup is darned expensive! I want to kill off a bunch of bermuda
grass to make room for a garden this year, and I understand this is
the only way to kill the stuff.

Is there something else that will kill the grass cheaper, but not
pollute the soil so I can grow vegetables a few weeks (or months
perhaps) later?

by the way, I'm planning to spray the grass to kill it...then cover it
with black plastic. Wait a few weeks for it to get warm enough not
to kill my tomatos then plant them (transplants from local nursery
stock of 5" or so plants) by cutting X's in the plastic about 6" and
planting the tomatos, then mulching right next to the plant.

Do I pose any problems to my plants by doing the above method? Does
the black plastic pose any risk of getting too hot for my plants?

Thanks!