How would you charge for consulting ?

I’ve been doing a side hustle as a data engineer with my old employer for about 2 years now. It started as a short term thing to bridge a gap, but I’ve enjoyed the arrangement and they benefit from it.

I charge $65/hr with minimum 3 hour shifts if I’m needed (job failures) or however many hours I choose to work. At first there was a decent amount of work so I’d invoice 40-50 hours a month. Now the work has slowed and I’m invoicing around 20 every month. I’m the only data engineer other than the director, so when they’re on PTO I’m responsible for monitoring pipelines and fixing if something happens.

Questions:

1. ⁠How would you charge for the monitoring when the director is on PTO? I’m expected to address failures, which aren’t frequent but do come up. I currently charge for fixing the issue (minimum 3 hours) but aren’t sure how to factor in my availability in case something happens. Watching for alerts shouldn’t be free.

2. ⁠Since this turned into a long term thing and the available hours have fallen, is it fair to suggest a rate increase to $100 / hr? This falls in the median-high band of some consulting rates for my area, aligns with my additional experience since first negotiating the rate 2 years ago, and helps make it financially worth while. Is $100/hr still too low?

Any other advice for this situation?

Thanks!