If your familiar with the company and the average pay scales for permanent employees and their related work loads, skill, and importance of what they do you may be able to come up with a fair estimate to what your permanent position pay rate should be.
Also If they offered you the position and you are not the one that actually asked for the permanent job that does give you some strong positive leverage.
If they came to you use the advantage. Set a realistic figure you want (but dont disclose it) and aim higher and let them think they worked you down.
The best job and highest pay I ever received was from a company that I turned down twice! The only reason I am still not there was due to corporate restructuring that closed down my department.
But my severance package payed for most of the expenses related to starting my own business though.
Keep it in mind that you may want to pad yourself in case of a restructuring as well. The permanence of a position can be far short of permanent.
A longer term work contract with a healthy severance pay package may very well be worth settling for. Ask for a good deal more than you want in the first place and just trade in that higher starting pay request as a bargaining chip to wards long term employment stability or at least a bigger pillow to fall back on.
Quality control is a very important part of creating a great product and a great company reputation. I think that makes it a rather valuable position!
Good Luck! I hope it works out in your favor!