NOTE: these rates are not set in stone and are only an average for this editor. The actual rate applicable to your document will depend on the depth of the edit, the quality of the writing, the topic matter, the proximity of the deadline, the length of the document and several other factors.
I communicated with Reader's Digest, GlaxoSmithKline, local and national newspapers, etc. for noted grammatical errors.
I started as proofreader in 1987 at the Bureau of Internal Revenue, Philippines, when given the assignment to proofread office memoranda, circulars and regulations before final printing and dissemination.
Since then, all official communication that needed proofreading passed through the office where I was assigned for final editing, from spelling to grammar. Fellow employees submitting their reports also consulted with me for their report-content, ensuring no grammar or spelling mistake was on their report, as this usually ended up at the Office of the Commissioner.
I spot grammar mistakes everywhere -- on advertisements, speeches, signs, brochures, leaflets, newspapers and similar printed material. When I joined an online course prior to leaving the Philippines to immigrate to Canada, I spotted grammatical errors in the learning materials provided by my Canadian facilitator, and I informed him accordingly. He then proceeded to have me review his material at the start of each new topic.
Although my major field of study in university was Accounting, my first passion is English and grammar, and to this day, spotting grammatical errors is so natural for me, it is like I doing it unconsciously.
Education degree
BS
Major specialization
Other, Accounting
Second specialization
English
First language
Other, Philippine
Areas of specialization
Not selected
Work experience
Present Occupation: Data Entry
Editing Experience in Years: 15
Scored 95% on editing test.
Test score 100% .
Test score 70% to 84%. 
Test score less than 70%.