First of all, as I'm sure you know, fully funded D2s only have 9 scholarships to offer to start with, so there really is not a lot of money there. If this school has a lot of returning players, there may not be money left. However, having that many players show up for "tryouts" cuts the odds down of your son making the team. My son plays for what would be considered a powerhouse D2. They do not take this approach. Generally speaking, they go out and recruit the guys they want and don't depend on tryouts. My son is a junior and this year is the 1st year they picked up a kid based on the fall tryout. I know they don't go thru 3 weeks of tryouts. I think they hold them for one day. The kid they picked up is a pitcher and will probably have a very limited role this season. Then again, his team has a roster of only 33. Last year it was 28, I believe with a couple of redshirts. I have seen D2 schools with bigger rosters as well as JV teams. That's something you may want to ask about with such a big roster - do they have a JV team as well. D2 teams do not have a roster limit like D1 teams do.
So, with all that being said, personally I think you would be taking a big chance of not making the team. 120 kids to be trying out is A LOT. Your son would have to show something exceptional wind up on the roster at the end of the tryout period. Think about it, between returning players and guys they went out and recruited, they may already have 30 players. There are 90 other guys trying to pick up the final 5-10 spots. Unless they carry a bigger roster. If they carry a bigger roster, you may be competing with 40-50 guys for play time if you make it thru the tryouts. You would have to be that much better than the returners and recruits to be able to take play time away from them. And if this school is a power house, it means that the players that they have are pretty darned good and you're not going to just run right over them.
I'm sure this school and coach have a sterling reputation. That doesn't change the numbers. I would be leery about this situation unless you just have no where else to go. JMHO.