How much do you charge for side work?

tl;dr - How much do you guys charge, and how do you structure it? Hourly, flat-rate?

I've got a good gig working 9-5 as a network engineer, but have gotten some opportunities for side work doing a small office setup (~70 users with simple needs, basically just need good wifi to get to g-suite). I've done the gun-for-hire thing before when I was younger in my PC Tech days, so I'm familiar with the risks and pitfalls of baby-MSP stuff. But it's extra money and I like money.

About me: CCNA, few years experience in government/enterprise and a couple years with a smaller company the private sector. Conversational in switching, weak on routing, reasonably familiar with Palo Alto firewalls, very comfortable with Ubiquiti wifi and Cisco WLCs.

I'm in the SF Bay area, for what it's worth.