Here's the thing...let's say you haven't published anything, you've only had critique from other unpublished members of your critique group, and you're not sure if you're ready to submit?
I'm not sure I'd spend more than $50 for this...but it BETTER be a significant length critique (i.e., 50 pages, in-depth, etc. for me to feel like I got my money's worth).
This may be an inexpensive way for you to get a better gauge from a more professional eye as to how you're doing as a writer, even if you don't place it yet, and way cheaper than paying a professional editor (which is a whole other conversation). It may also tell you whether you're getting good, constructive, and worthwhile feedback from the people who are currently critiqueing you (if any). It's a nice gauge, at not too steep a price, to figure out where you currently stand, and what some of the professionals seem to think of your prose.
Suffice it to say, set a price limit on what you're willing to pay for it, if you think it would benefit you as a writer, or in submissions or both. Don't expect that a critique will garner you a request for pages, although that's a nice bonus if it happens. It may be enough for them to remember you when the project's complete, or just another networking contact familiar with your work.
I've been to several conferences where I paid the few bucks extra for the critique, and ended up not only with in-depth comments, but also new friends and mentors. That's a pretty good result, too.