As you would imagine, the amount of pay for tech writing jobs can vary widely, depending on the company and job requirements. I've been a tech writer (contract and permanent) for 16 years.
$30 per hour for your first tech writing job is not bad, especially if you are being paid under a W-2. This setup requires your temp employer to pay their half of the Social Security tax; otherwise, you have to pay it. It may also qualify you for unemployment benefits, assuming you work there long enough. On the other hand, if you are considered fully self-employed, you can have more tax deductions, but I've found it nearly impossible to make it worth my while. Your situation may be different.
You can make a lot more than $30 an hour as a tech writer, but also a lot less. For example, if you have pharmaceutical experience, the salary potential is great. The lowest contract rate I've received is $25 but sometimes one has to do it in order to keep working.
In your next tech writing contract job, go for $35, at least, or much higher, and see what develops. Depending on the cost of living in your area, you may be able to get much more. The more job experience and knowledge required for the job, the more salary should be offered.