It all depends on your particular niche.
If it's a hot new field with few experts, then you can name your price. If it's a common segment and there are a lot of people (even if they just look good on paper) trying to move to the tech writing/editing side, then they'll often work for nothing just to get the credit—bringing the perceived value of the work down for everyone.
Do you know people who are currently working in the field as authors or editors? Ask the authors to introduce you to their editors. Ask the editors if they're hiring freelancers and what their pay rates are like.
My experience (having done tech writing & editing since 1997) is that the field is a trailing indicator of the economy. That is, if the economy has been going up for the last n months, the writing biz will have been good for at least the later part of that time period. If the bubble then bursts, writing takes the hit ~six months later. The result: you're always trying to figure out what's about to be popular, but your gigs are based on the economy of a few months ago.
So, how have the economics of your tech niche been for the last few months? That should give you an idea of what the writing side will be like for the rest of year.