> The only hard part is determining what your labour is really worth - this can take a fair bit of effort, research and soul-searching, but is an absolutely essential prerequisite to negotiation.

I disagree. I think the intrinsic value of labour is not necessary to consider when calculating what you should be paid. The golden rule is: you're worth what people will pay you.

I think you need three numbers: how much you need to be comfortable (i.e. you have a budget for living expenses & savings goals); how much the market is paying for similar positions; how much value you will add to their company.

The first number is your low-end: you can't accept an offer under it, and you'd accept an offer around it to build your skills, experience, and networking. The third is their high-end: they can't pay more than you bring in or else they'll go bust. They probably don't know this number, their budget would be set based on market rates.

Your job as a candidate is to find positions where the market rate is above your low-end, and then identify the areas where your skills & experience will provide more value to the company that they expected, so they can better calculate their high-end & are willing to negotiate up accordingly.