Perhaps just check weight - 120AH will be a heavy sucker
Having a quick look around a decent 120AH AGM is around or above $200, a decent battery box is easily $65 (and that ones seems to have some practical useful fittings on it).
I'm not a guru on brands or chargers, but 12A capacity is more expensive generally and handy if you only have an hour or two access to a friends genny (versus say a cheaper 4A or 8A unit). Would expect over $100 for 12A or greater charger.
So all up sounds like a fair deal from what is described.
Can seem like a lot of money, but you can easily get close to this going through a couple of "jumpstart" power packs that often have 15AH or less batteries in them, and aren't designed to be drained significantly or for any period of time - typically $100- $150 each.
Perhaps check the warranties and reviews, but sounds like something that should last years if looked after.