No they're probably not worth it.
If they won't spend a moment of their time with you without charging you, stay away. If they don't want to be a mentor, run.
Frankly when I was learning to fly my CFIs were young guys who wanted to be airline pilots. They were motivated, real and they didn't charge me for ground. I had a different instructor later, older Lt Col who wanted to be an airline pilot, he was awesome too and spent a lot of time at the airport with me off the clock. I felt with these guys like we were all in it together and they certainly had a passion for flying. Flying > Money.
I decided that was the kind of CFI I wanted to be. Save your money and put it into flying because after all we're there to fly. When I instructed from 97-00 my school charged $25-$35 per hour for me and paid me $5.50-$7/hr. I didn't charge for ground either despite doing full blown ground session. I wanted that time to focus on learning and not have a student have a clock running in his head trying to calculate how much this was costing him. I wanted them to get it, and if they weren't getting it (but trying) then I needed to keep attacking it from different angles until they got it. The point was learn. And the better they learned the less time we wasted in the plane and they got done on time and on budget. But at my school we'd solo guys in 5-10 hours and private and instrument ratings were done in the min time or something was wrong.
Of course sometimes we grabbed a football and went out back and tossed that around while doing ground and a white board wasn't necessary, but hey, that's what you get when it's free.
You can have very good CFIs for cheap. I've met the $100/hr CFI here in Atlanta recently and I can tell you they weren't worth a dime of it. Give me the kid with 300-400 hours that has a lot of enthusiasm. The 600-1000 hour CFI has enthusiasm and experience and the 1200-1500 has a lot of experience and little enthusiasm. You do burn out if you put a lot into it. Just do.
If a CFI doesn't give a damn about anything other than your credit card then don't give a damn about them and move on.