You really only have two choices worth considering, #1 and #2, #3 is a
mess.

#1 It should be easy to get the spots to the uniform depth required
with a hoe, rake and some topsoil. Then you can lay new sod. The only
real disadvantage might be if the available variety has any difference
in color from what's there now to the point that it's noticeable.
Unless you have a large area, cost shouldn't be too much. Advantage is
results are fast

#2 This will work too, but takes longer. When laying lawns from plugs
they are spaced 12-18 inchs apart, so with 1-2 ft holes, they will fill
in fine on their own. Personally, unless I was looking for fast
results, I'd go with this approach. Make sure to fertilize at the
appropriate times to encourage faster growth.