Have a clear understanding of your identity, mission, direction, goals.
Have a clear understanding of what you're looking for in a hire.
You're looking for someone to be a fit to what you're doing as much as they are looking to be apart of something that is a fit for them. Pay, product, culture, and various mix of expectations and what each side wants is what makes this works.
You'll want to be as clear as you can about what's exciting about what you're doing, where you're going with this, and who you're looking for to join you on this journey.
They likely are getting underpaid compared to their peers at a tech company.
The downside is, a "senior software engineer" at a non-tech company might not be quite the same level as a "senior software engineer" at a tech company. I say this as one of the former myself.
I'd say search on your friends network first. If it is hard to find on your network then I suggest Angel.co, stackoverflow.