proofreading rates advice?

[sybness]

Hey all--I have been asked if I want to proofread four journal articles (7,000 - 8,000 words each). The job is straightforward: no fact-checking or formatting (beyond ensuring the text adheres to the Chicago style), just checking for writing errors (spelling, typos, etc.) The last time I did this kind of work on other people's stuff I was paid €600 for 4 long chapters from a PhD thesis; I'm thinking considerably less for this job, obviously.

Any thoughts or sites I can check regarding standard rates? Many thanks, in advance...