Well just like anything else there are a ton of opinions on what is best. If your son has been saving that long then I would buy him a reliable vehicle. There are nothing wrong with YJ's but it is hard to find one with low miles. To be honest it is hard to find one more than few years old that doesn't. People drive Jeeps.
I think looking at a TJ is the right thing to do. TJ's have coil springs over leaf spring which quit being on wranglers in '95. Looking at a TJ from 2000 on is also a good because they have a coil pack versus a distributor. Somewhere around that time they changed the soft top material to sail cloth which is quieter. I prefer a soft top so that is a good change to me.
Without question I would buy a 4.0 jeep. A 2.5 is a 4 cyl. and not to offend anybody they are underpowered....especially if your son decides to go up in tire size.
Now I have no idea what a Rocky mountain edition is. To be honest I am a CJ guy. So everything I just recommended I dont have.
But based on local prices and the fact that isn't really bad on miles IMO I would say that a price between $8k and $10k would be a good price for this time of year. That is assuming the top is in good shape, good tires, etc. Rubicon TJ's are starting to come down a little in price and have seen some with similar mileage that could be bought for the $12.5k range. They are going to hold their value...especially if kept kinda stock.