It's difficult to quote a price over the phone. How much do installers charge in your town? What are the dumping fees to get rid of the old tub? What's the cost to rewire and redo the plumbing?
Like any home renovation, nobody can quote an accurate price on a job until they see the job site and know what work is necessary.
You don't want to buy a walk in tub and find out later that you're stuck with extra costs that weren't quoted to you in the first place.