In ECDSA, how many field operations are used for signature verification?
Usually, the interleaving of wNAFs is faster than Shamir's trick for simultaneous point multiplication.
Using interleaving with window sizes 5 (fixed) and 4 (random), the total number of operations is roughly (taken from Hankerson et al's Guide to ECC)

$(0.37t +  3)A + (t + 1)D$

where t is the bitlength of the scalars (which should be the same as the bitlength of the field size for standard curves), A is a mixed point addition (projective + affine) and D is a point doubling.

For standard prime curves with $a=-3$, using Jacobian coordinates, we have (from the EFD):

$A = 7M + 4S$,

$D = 3M + 5S$,

where $M$ is a field multiplication and $S$ is a field squaring. Therefore,

$M = (5.59t + 24)$,

$S = (6.48t + 17)$.

For the 128-bit level of security, if I got everything right, $t=256, M = 1455, S = 1675$.