I find that college professors are one of your best resources. Take it to a pre-dental/per-medical advisor/committee if such a thing exists at your school.
Family and close friends tend to ease up on the critique to spare your feelings, or maybe since they've gone through that experience with you, they might understand what a stranger may find confusing. (That sentence right there was downright confusing itself, sorry).
Don't waste your money. Heck, if you want, I'll read your essay for ya. =)