Or, it's like $7, try some of the Proraso pre / post shave cream.

When I first started straight shaving, I definitely got a lot of irritation on my neck area, a big red blotch on both sides of my neck.

Two things I figured out, 1) at first, the pre-shave cream really helped, and 2) and this might apply to you, I realized that I was lathering far further down my neck than I needed to, when in fact, my beard ended further north. So I adjusted where I put the blade on my neck, stopped shaving so far south, and that immediately improved my shave. So have a look at where your beard line in fact ends, and only shave that area.

Could be a combination of #1 and #2 for you, but for me, the big one was #2, shaving farther down my neck than I needed to go...YMMV.

Good luck and let us know how it works out!