If I was hired to do the job I would:
1 spray the whole lawn area with finale.
2 wait 2/ 3 days for the finale to kick in.
3 spread 10+ yards of topsoil and lay sod.
4 Fertilize with 16-16-16 , water and hand you a bill 80)

As far as tarps and the like go... It takes quite a while for tarping to
kill off perennial weeds. Time is something that you do not have so
spraying will be your only true option. Dandy lions and other perennial
weeds can and most likly will work their way up through the sod over time.
I personally wouldn't chance it and would take the extra effort to do it
right the first time.

Btw, what they charging you for sod out there..?
Good luck to ya.......

Makes sense. I'll just spray either Finale (can't find it?) or
Weed-B-Gone and wait a week or so, cover it with top soil, and sod
over it.

For sod, they're charging somewhere between $3-4 for 9 sq. ft
(6'x1.5'). So, for ~1400 sq. ft. I'm looking at (my initial guess was
off), the sod alone would be ~$600. Not sure how much top soil would
cost to cover the area.

Does anyone know where to get top soil in Massachusetts?