A good trainer can help you achieve goals. Trainers make from around $8.00 hour + spiffs (for pushing snake oil) at 24 Hour Fitness, to $12.00 hour at LA Fitness, to around $25.00 at Lifetime on up to around $90, or more, in some private places.
I have two personal trainers that I work with from time to time: Sagi Kalev here in Dallas, and Jesse Leyva, of Flower Mound. Anyone who is anyone in fitness knows Sagi, because he's been on the cover of Muscle and Fitness more times than any man alive, and is regularly on the cover of a 1/2 of a dozen of other magazines. Because of my outstanding ability, Sagi offered to train me for free, but, we didn't ask him to do that. Sagi and I are friends, share similar outlooks, and I learned a lot about high-level bodybuilding from him that fast-tracked my stage presence and confidence. I've never placed lower than fourth using Sagi. Sagi owns Energy Fitness in Dallas, and, if you're in the area, feel free to stop by and say hi to Sig, Josh, and Josh, and tell them Chuck sent you. They'll know immediately who you're talking about. Jesse is a very good friend as well, and like Sagi, has a bunch of trophies, and has trained champions. Jesse helps me with choreography, and stage presence, the parts that are hardest for me. Jesse is a nice guy, and Logan (flex89) and I are helping Jesse to get ready for the Ronnie Coleman Classic here in about 10 weeks or so. Jesse is always "on" (positive mood) and is a real treat to be around. Over the years, we've become good friends. For my diet, routines, and training method, I train myself. After 33 years, I have a pretty good idea what I'm doing, although, from time to time, I'll stumble across a better idea than someone might have. Neither Jesse, nor Sagi, prescribe HIIT (High Intensity Interval Training), but, I've found it works absolute wonders for me. Sagi always hugs me at public events and "how you Chuck?" etc. Sig is from Saudi (I mean Israel) and is a lot of fun. He's one of those guys that whatever he touches he's successful in.
Logan and I have another friend, Justin, who is so intimidated by the gym, that he WILL NOT train without a trainer. We kinda' laugh to giggle that even after being in the gym a couple of years, he won't lift without his "trainer." Justin is likely a closet case, and he has all the typical drama and baggage that those folks have. It's sad, and we'd like to see him do better, but, he's not budging.
Trainers can bring another viewpoint to your training, but, many are CLUELESS, have no practical experience, no proven success, and paid $900 for a cert from, say, NASM, which is all about core training but doesn't teach them the skills that, say Jesse or Sagi, have.
Some folks find the gym a scary place, and don't have a friend train with, or are to lazy to conduct their own research. Those folks clearly can benefit from a trainer, if it gets them more confidence, and know how.
Like everything else, the money is all relative, and the "is it worth it" question is all relative. In my case, of competing at the national level, I'm convinced Sagi made a LOT of difference because he knew a lot of the tricks of the trade. For a casual lifter, or someone intimidated by athleticism, I'm not so sure the trainer makes so much difference.
If you hire a trainer, you'd be wise to hire one near middle-aged, who has both practical experience, and book knowledge, as well as more human relations skills. I wouldn't hire a cute 18 with a cert for any serious training. They are to young to realize how little they truly know.