That sounds reasonable. To add to TorquayFan's answer, my current 35-40a battery was 1,500 baht from a high street shop, and from Honda I think is 2,000+, but they give a 2-300 baht refund so it comes out somewhat less than that. Your battery may be a bit bigger so 1,800 sounds about right.
Have no idea whether sealed or not, but I figure it's not worth worrying about - just buy a new one every three years (preferably before you get stranded) and be done with it.