Any advice appreciated:

I am looking at advertising in national press with some cheap rate advertising they are running at the moment.  Various publications ranging from 400,000 to 1000,000 readership.

I realise this is going to depend on so many factors, but does anyone have a good idea of what average response rates are for the national press (or any other printed media)?

I basically have no clue what to expect and obviously do not want to spend out on a 'tets' campaign only to have it fail abysmally.

Thanks a lot