My son did a G/T program at the local state university for a few years. It was $1500 for a three week summer program of 1/2 days. We thought he needed the exposure to kids "like him" and some classes that we couldn't provide. We stopped because it wasn't worth it after the first couple years. Not sure it was worth it even then, but he did get a lot out of it and it was good experience for him. I think at this point, we'll go right to the CC if he wants to take outside classes. Even at full price it would be cheaper.
One, ds doesn't really care that much about being around similar kids. He's 2E so he didn't have a ton in common with some of the kids anyway, but he's a very strong introvert and being in class 5 days a week, even just 1/2 days, even just for 3 weeks, was pretty hard on him. He actually wants to do as much of college as he can online. He does enjoy our 4-H STEM club - lots of quirky kids who like STEM, many gifted, and it's only twice a month.
Two, they changed how they were set up so all the kids in a certain age group had one assigned course that all took, then could pick two additional selections (for the 1/2 days). Ds has pretty specific interests and the last summer he went, we registered very early so he could get the classes he wanted. They ended up moving one of his selections to the afternoon only, so as a 1/2 day student he couldn't take it, and he ended up in his 3rd or 4th choice class because of the timing when they did it.
Three, they put 7th through 12th graders together and the class selections were a lot of stuff ds has no interest in. SAT prep (we're not looking for him to take it quite yet), accounting (no interest), stock market. Ds's interests run to programming, robotics, building.
Four, some of the classes he did take were things that we are doing in our 4-H Club.