I'm assuming this is as a self-publisher given the Amazon comment. If the money you would spend is all the money you have, don't do it. Don't quit your job. Don't mortgage your house. Don't use up your life savings. Most self-publishers won't make it back, so make sure you'll be fine if you never see that money again.
If you do have some money to spend on self-publishing, the first thing is to make sure the product is good. Being able to hire editors, get proper cover art done... those are all useful things. There's no point in promoting a product that isn't ready.
Publicists are something I'm rather dubious about though. It'd be rare to find a good publicist who is open to self-published clients. Those that are will be selective. Which means what is usually happening is people offering services to self-publishers aren't really that good. They're either doing nothing much or doing things the author could have done. I'd be very careful about this.
Which isn't to say that it's bad to spend money on promotion if you have the money to spend, but you might find you get more for the money by running adverts, putting review copies on NetGalley, etc.