Based on what we pay for field trips, I think it's expensive. Usually, my only fee is busing, and that is $5 per field trip. The field trips never include food. Either the kids pack lunch or they can buy a packed lunch from the cafeteria for the same daily cafeteria rate (under $2).
So I think it's expensive.
If the field trip is still cheaper than the other orchids, then maybe there isn't a conflict of interest. I just don't know enough about the rates of your area.
That's a lot more than we pay, even given apple orchards do charge to pick. But wait- what are they doing at the orchard if they aren't picking apples? And if they are, where do the apples end up?
We paid less than $15 this week for my son to get bussed 20 miles each way to a kids' science museum for the day, including admission. I suspect a lot is subsidised by the PTA and your PTA maybe can't do that?
There could be a conflict of interest, but it's hard to know because you don't know the % of the cost that's the bus, or the total cost for this orchard or the other 2.
It DOES sound like an excellent trip though. Apple-picking is excellent fun.
How much would it cost at the other Orchards? If she is offering fair/competitive rates, it wouldn't bother me. If others are cheaper or have an overall better package for the same price, it would be a huge conflict of interest.