Juanse,
Honestly, if you have a limited budget, you're better off spending that money on GMAT prep services because unless it's 700 or more, you're going to be a stretch for the top schools. Any consultant who tells you otherwise is simply giving you a sales pitch and not being honest with you. Of course there are a small handful of folks who get in with GMATs outside the middle 80% (which at top 16 schools are around 660-760, and some are even more than that at 680-760), but it has much more to do with the applicant's individual extraordinary circumstance.
Here's another way to put it. There are enough applicants out there whose profiles (including their GMATs) are in range, and yet these people still don't get in.
What has changed especially in the last few years is that the variance in overall caliber of applicants has really narrowed. It makes it even more subjective - and yes, having a consultant (and getting feedback from friends, family, colleagues, etc. in addition to that) can certainly be valuable, but not if your basic stats are out of range.
Here's another way to look at it. Admissions consultants are like personal trainers. Like personal trainers focus on only *one* (but important) aspect of your overall health goals, consultants can only coach you on *one* aspect of your overall profile (and that is how well you execute the applications and interview). Just like no amount of fitness/exercise programs you get from a personal trainer is going to do you a whole lot of good if you're not eating right -- admissions consultants can't give extracurriculars you don't have, or get great jobs for you, or get you to attend a prestigious undergrad. And any consultant who tells you otherwise is akin to selling you "ab machines" that claim you can get six-pack abs on exercise alone.
Again, just like personal trainers can be *invaluable* when it comes to your fitness goals, admissions consultants can also be the same way in the admissions process. But they are only useful if taken within the context of the whole.
