Keeping it simple
Most proofreaders' websites I visit require the client to get in touch to receive a quote, and involve a complicated formula based on an hourly rate, amount of corrections and length of the piece. They might even require a sample from the piece to calculate all this.
I've kept things simple so you can more-or-less instantly see what I will charge to proofread your piece:
Grant application (2,000–5,000 words)
£75, two-day turnaround
Journal manuscript (4,000–8,000 words)
£100, three-day turnaround
Thesis chapter (8,000–12,000 words)
£150, four-day turnaround
Master's thesis (10,000–20,000 words)
£200, five-day turnaround
PhD thesis (60,000–80,000 words)
£400, ten-day turnaround
Book manuscript (100,000–120,000 words)
£600, fourteen-day turnaround
If your piece falls outside this word count, or will require a truly substantial proof, the price can be adjusted. This also excludes reference checking, which can be an addition.