$28 a page is pretty expensive.
No, it really isn't. It's all relative, I suppose, but here's the deal: there are ESL writers who do this full time and can live like kings earning $17/page (this is assuming the writer gets 60% of what you pay, which is a fair rough estimate), and there are native writers who do this very part-time and usually rather fleetingly who might be OK earning this as their sole source of income for a short time or as a supplement to other sources of income, but as a long-term job this rate simply isn't going to cut it for anyone of intelligence and drive (i.e. the people you want writing your paper).
Given that native writers have to pay pretty high taxes on what they earn (I pay a little under 20% of everything I earn to the government, not counting sales tax), the real earning rate of the $17/page drops to about $14/page. Assuming your writer can research/write an average of three pages an hour, you're looking at $42/hour (not counting the time spent messaging customers and dealing with other miscellaneous tasks). Doesn't sound too bad, and it isn't terrible, but then there's all the things that a "real" job gives you that this one doesn't--health insurance, a retirement plan, some semblance of security, etc. Then there's the fact that the job is highly seasonal, so if you don't earn enough in the spring to get you through the summer you have to find a new job, and chances are the people that are good at this are tired of working as baristas (I know I was).
Anyone that is truly intelligent enough to do this work well coud go find an office job that would ultimately lead to better security and a higher salary, and a more stable income. So the good writers either charge more or move on. $17/page is a possible summer rate for a good, full-time writer, but it simply isn't going to get you top quality during the busy season.
Remember, expense is relative. $10 is an expensive Big Mac, but $20 is a cheap filet mignon. Maybe you can't afford the steak on your budget, and it's good to have that level of knowledge and control over your finances, but that doesn't make the steak over-priced.