NYC real estate brokers who specialize in rental apartments generally charge between 8.5% and 17% of the annual rent (the fees tend to be higher in Manhattan; less in the outer boroughs and in New Jersey), so hiring a broker to do your research can easily cost you several thousand dollars. For example, the broker's fee for a typical Manhattan apartment that costs $1500/month is $2700
Source: Urban Edge No fee rentals
And that's my experience as well ... I have a friend here in Atlanta who is licensed in NY ... just flew out today to show a commercial property .... She tells me that even at the low end the brokers fee is is almost never LESS than 1 month's rent
BUT your instincts are good, in my opinion... this is NOT something that necessary ... as a matter of fact, many rental brokers here is Atlanta move on VERY quickly if someone doesn't take the first apartment they show them ... it's very rare to find what the model is SUPPOSED to be; working hard with a small number of clients, to find what they need. To most brokers it's a numbers game ... somebody will eventually take the apartment in question.
I think your instincts are also good, that if you have some time, there's just NO reason to use one (UNLESS, MAYBE - and this takes time as well - you find a really good one, through word of mouth, that has really WORKED for someone, that really does represent YOU)