Considering launches from the two major cosmodroms are launched into inclinations quite far from equatorial, and that inclination change in LEO is awfully expensive in terms of delta-v, what trajectory do rockets take to deploy satellites into a low orbit above Earth's equator?
The answer is that they do not, the delta-v cost is as you state high. Plesetsk is 63 degrees north, and Baikonur is 43 degrees. Plesetsk is actually so inclined that it costs less to do a bi-elliptic manoeuvre, meaning that you accelerate almost up to escape velocity, do the inclination change at a great distance, and then fall back and brake into low Earth orbit. To have a satellite in low equatorial orbit, you have to launch from the equator or close to it.
For that matter, almost no satellites are launched to equatorial LEO from Cape Canaveral either.