There is no single number, because it depends on how much of the person you need and for how long, but it is easy to reason about. Fractional senior technology help is usually bought by the day, a day or two a week rather than full time, which is what makes it affordable for a growing business that could not justify a full-time hire at that level. The thing to watch is not the day rate. It is what gets added on top of it.
What actually drives the cost
Four things move the number: how senior the person is, how many days a week you need them, how long the engagement runs, and whether it is advisory or hands-on delivery. A short fixed-scope review sits at the low end. Ongoing delivery, where the same person is building and running things, sits higher. You scale the cost by scaling the days, which is the whole point of fractional.
The premium to avoid
The cost most people miss is the recruiter premium. An agency typically adds a percentage, often around 18%, on top of the day rate, for the introduction. Hiring direct removes it entirely. On a multi-week engagement that is real money that goes to the work instead of the finder.
Day rate is the wrong thing to optimise
The expensive mistake is almost never the day rate. It is the wrong decision: the system replaced that should have been fixed, the platform bought that nobody needed, the year lost going the wrong way. A senior person who gets the big call right is cheaper than a cheaper one who gets it wrong. Judge on judgement, not on the rate.
How to keep it predictable
Start with a fixed-scope engagement, so you know the total before you commit, rather than an open-ended retainer that drifts. You get a usable result inside a known budget, and a clear decision about whether to continue.
A Technology Discovery and Blueprint is deliberately shaped this way: fixed scope, known shape, a plan you own at the end.