Just read a thread elsewhere about a person who was offered a job she wants but cant afford to take because the starting salary is too low.
I have never accepted a professional job where I did not do some negotiation. The admin/HR department of employers (especially in accademia) often try it on by offering new starters the lowest point on the grade. Most often they do not really understand the technical requirements of the post and therefore do not understand how well qualified one is. They simply see one as a new starter. I have always gone back and argued that I had a higher quality degree, previous experience, a record of publications or whatever I considered made me a good fit for the post.
The worst that will happen is that the employer will refuse to budge. If you were going to have to refuse the job anyway for financial reasons what have you lost? Nothing.
Naked pair enjoy meal in non-naturalist pub.